An easy way of obtaining a green card is through a family member who is a US citizen or a green card holder. US citizens may sponsor their spouses, children, adult sons and daughters, parents, and brothers and sisters for lawful permanent residence. US permanent residents are limited to sponsoring spouses, children and unmarried adult sons and daughters.
Except for spouses, children and parents of US citizens who are deemed immediate relatives, all other categories of relatives are subject to a numerically-limited preference system. It may take quite a while to obtain a green card if one is subject to the preference system. The time taken depends upon one’s nationality and relationship to the US citizen. The process is a lot faster for immediate relatives.