There are two broad categories of visas, one Non Immigrant or Temporary Residence Visas and the second is the Immigrant Visas- Permanent Residence Visas. To qualify one would need to satisfy certain parameters as laid by the immigration authorities, a few of the categories are given below:

Green Card

GETTING A GREEN CARD THROUGH RELATIVE
The applicant qualifies for a Green Card if he or she has a close family member who is a Citizen of United States or Green Card holder of the same. You can qualify for a Green Card through relatives if you fall into one of the following categories:
immediate relative of a US Citizen
preference relative of a US Citizen or Green Card holder, or
accompanying relative of someone in a preference category

GETTING A GREEN CARD THROUGH AN ADOPTION

To obtain a Green Card through adoption, it must take place before the child is 16 years of age and that he or she has lived in the parent's legal custody for two years before applying for the green card unless the child is an orphan.

GETTING GREEN CARD THROUGH AN ADOPTION OF ORPHANS

A child may obtain a green card as an orphan only if a US citizen is adopting him or her. A child is an orphan if both natural parents are either deceased or have permanently and legally abandoned the child.

GETTING GREEN CARD THROUGH YOUR FIANCÉ (E): K-1 VISAS

If you intend to marry a US citizen, your fiancé may bring you to America for the wedding through K-1 visa. It is a nonimmigrant visa but it can be converted into a green card. The Beneficiary and their minor dependents may come to USA in order to marry a US citizen

GETTING A GREEN CARD THROUGH EMPLOYMENT

In order to qualify for a green card through employment:
you must have a job offer from a US employer
you must possess the education and experience relevant to the job offered, and
If you are already in US, you must be in valid legal status.

The following categories may seek to obtain an Employment based Green Card based on the following order of preferences

first preference as priority workers
second preference as workers with advanced degrees or exceptional ability
third preference as skilled or unskilled workers without advanced degrees
fourth preference as religious workers and various miscellaneous categories of workers and other individuals
fifth category as individual investors willing to invest $1,000,000 in a United States business or $500,000 in economically depressed areas

GETTING A GREEN CARD THROUGH INVESTMENT

US Green cards can be obtained by making an investment, anyone who invests a minimum amount of 1 million US dollars by setting up a new business or expanding one that already exists. The investor must be active in the management of the Company. The required amount of the investment may be reduced to $500,000 if the business is located in rural area.

GETTING A GREEN CARD AS A SPECIAL IMMIGRANT

Special immigration green cards are available under different situations to the people who are
The workers for recognized religious organizations
Foreign medical graduates who have been in the USA for a long time
Foreign workers who were formally long-time employees of the US government
Retired officers or employees of certain international organizations who have lived in the US for a certain period of time
Foreign workers who have been an employee of the US consulate in Hong-Kong for a minimum of 3 years
Foreign nationals who have been declared as dependent in juvenile courts in USA

GETTING GREEN CARD THROUGH ASYLUM

To qualify as a refugee, you must have an experience of persecution in the past or have well founded fear of persecution in the future in your home country on the basis of race, religion, membership in a social group, nationality or political opinion.

GETTING H-1B VISAS

To obtain H-1B Visa, there are four requirements that needs to be met:
you must be coming to USA to perform services in a specialty occupation with a college degree or its equivalent in work experience, or to be a distinguish fashion model
you must have a job offer from a qualified US employer
you must have a valid background to qualify for the job you have been offered for

GETTING H-2B VISAS

You can qualify for an H-2B visa if you are come to USA to accept a temporary or seasonal non-agricultural job from a US employer and you have the valid background or skills or abilities required by that employer.

H-2B visas are aimed at skilled and unskilled workers, compared to H-1B visas, which are intended for college-educated workers. To get an H-2B visa, it must be proved that there is no qualified Americans available to take the job you have been offered.

GETTING H-3 VISAS

You can qualify for an H-3 visa if you are coming to USA for on-the job training to be provided by an American Company. The purpose of the training should be to improve your skills in your career in home country. Similar training opportunities must be available there. In that case there are no quota restrictions.

GETTING L-1 VISAS

You qualify for an L-1 visa if you have been employed outside the USA as a manager, executive or person with specialized knowledge for at least one year, and you are transferred to the USA to be employed in a position that utilizes your special knowledge and skills.
The purpose and design of this Visa is to provide practical guidance to the foreign business owner, executive, or manager in establishing a United States branch or subsidiary of an existing foreign business.
The initial visa granted to a non-US business owner who is a manager or an executive is known as the L-1A visa, and is granted for a period of twelve months. It is a temporary visa, and not to be misunderstood with permanent residency, which confers a permanent immigration status with far greater implications.
The initial twelve-month L-1 period is reserved for those instances in which the subsidiary or affiliate office in the United States is newly created or functioning for less than twelve months.
It should be noted that this visa could certainly be processed in a number of different ways, using different forms of corporate relationships (for example by purchasing an existing business, or entering into a strategic partnership with an existing business or establish a new business). But, by and large, the most commonly used formula involves the creation of a new entity in the United States, which will serve as the base of operations for the foreign executive or manager to initiate operations in that new market.

GETTING E-1 VISAS The E-1

classification is authorized for a national of a country with which the United States has a commercial treaty, who is coming to the U.S. solely to engage in trade of a substantial nature principally between the United States and the alien's country of nationality. The trade involved must be international exchange (successfully negotiated contracts binding on all parties) of items of trade between the U.S. and a treaty country. Title to the trade item must pass from one treaty party to the other.

GETTING E-2 VISAS

The E-2 classification is authorized for a national of a country with which the United States has a commercial treaty, who is coming to the United States solely to direct and develop the operations of an enterprise in which he or she has invested, or is actively involved in the process of investing, a substantial amount of capital.

The alien must demonstrate that he controls the enterprise by showing ownership of at least 50% of the entreprise, by possessing operational control through a managerial position or other corporate device or by other means.

GETTING STUDENT VISA : F-1 AND M-1 VISAS

If you are coming to USA to study full time in a program leading to a degree, diploma or certificate, you must be entering a US government approved school to qualify for a visa. You have enough money to study full time without working. You must be able to speak, read and write English well enough to understand the course work. You must prove that you intent to return to your home country when your program of studies is over. Both F-1 and M-1 visas are issued for the estimated length of time it will take to complete your proposed program of studies. M-1 students will receive a maximum period of one year. F-1 students will last longer than vocational or non-academic programs for M-1 students.

GETTING EXCHANGE VISITORS: J-1 VISAS

You can meet the requirements for a J-1 exchange visitor visa if you come to USA as a student, scholar, trainee, teacher, professor, research assistant, medical graduate or international visitor who is participating in a program of studies, training, research or cultural enrichment specifically designed for such individual by the United States Department of State through its bureau of Educational and Cultural Affairs (ECA). You must already be accepted into the programs before you can apply for the visa. You must have enough money to cover your expenses while you are in the USA as an exchange visitor. You must have sufficient knowledge of English in your subject and you must intend to return home when your status expires.

GETTING O-1 VISAS

The persons of proven extraordinary abilities in science, arts, education, business or athletes, outstanding professors and researchers and multinational executives or managers are eligible for O-1 visas and do not require labour certification.
Evidence of internationally recognized prizes or awards.
Membership in an association in the field for which requires outstanding achievement of their member, as judged by recognized national or international experts.
Published material about the person in professional or major trade publications or other major media. Participation as a judge of the work of others.
Evidence of original scientific, scholastic, artistic, athletic or business-related contribution of major significance.
Authorship of scholarly articles in the field.
Artistic exhibition or showcases.
Performance in a leading or cultural role for organization that have a distinguish reputation.
High salary in relation to others in the field.

GETTING P-1 VISAS

Entertainment companies that have been nationally recognized as outstanding for a long time are eligible for P-1 visas. P-1 visas can be issued based on the expertise of a group. P-1 visas are not available to individual entertainers but only to member of group with international reputation. Evidence of that reputation must be shown with the following:
Proof of one year performing
regularly employed by the same group
group's international awards or prizes
group's leading role in production
groups published material showing the outstanding achievements
proof of large box office receipts or ratings (commercial or critically acclaimed successes)
proof that your group commands a high salary.

GETTING R-1 VISAS

The R-1 classification applies to a religious worker. this is an alien coming to the U.S. temporarily to work:
as a minister of religion,
as a professional in a religious vocation or occupation, or
for a bona fide nonprofit religious organization at the request of the organization, in a religious occupation which relates to a traditional religious function.
The applicant (religious worker) must have been a member of a religious denomination having a nonprofit religious organization in the United States for atleast two years immediately prior to the application date. To be eligible, the U.S. petitioning organization must be a nonprofit religious organization granted (or eligible for) tax exempt status, and must demonstrate that it can and will provide for all of the R-1 beneficiary's financial and physical needs.