Now, your SO has landed on U.S., what to do next?

If you are holding on a K1 VISA, you need to:
-Get SSN
-Married in 90 days
-File in I-485 for adjustment of status (AOS)
Note: the I-94 you get at the airport allows you to work in that 90 days but llots of places won't hire you as they don't want to risk hiring somone illeagal. However, after the 90 days and before you get your temporary green card, you need to file in I-765(EAD) for work permanant if you want to work. And you will also need to file in I-131(AP) for advance parole if you plan to leave the country before your green card issued.
File online: click here
Documents you need for AOS:
Forms: I-485, G-325,noterized I-486,I-693, and check
Others: Two passport-style photos; Certified copy of marriage certificate; Birth Certificate for the foreign spouse;Cope of I-94 (both sides) ; Cope of visa and U.S entry stamps; Copy of passport for the foreign spouse; Copy of I-797 (P2 of K1) 129F (NOA2); Certified copy of divorce certificate; Sponsor's Bank Statement; Sponsor's tax return and W2 for last 3 years; Other financial evidences

If you are holding K3, you can choose to go back to your country and wait for your permanant residence there or file in I-485 within the 90 days.

For CR1 holder, things are lot easier. Once you enter into U.S., your green card will be mailed to you within four weeks after your arrival. You can also upgrade your CR1 to IR1 if you have been married more than two years.

Forms:
USCIS form I-485(AOS $325 for age 14-75, $225 for age 14 or less, additional $70 for finger print)
USCIS form G-325A
USCIS form I-765 (EAD, $180)
USCIS form I-131 (For K1 only, $170)
Notarized I-864
USCIS form I-693 (click here to search for a Civil Surgeon in your area.)