The infamous affidavit of support (or I-864) is a document that legally binds you with your spouse in a very strong manner: the American spouse declares financial liability for the sponsored spouse for the next ten years (even if you get divorced) or until the foreign spouse obtains American citizenship.

Also, if your spouse's income (or the both of your incomes combined) does not satisfy the American requirements for the I-864, make sure far ahead of time that someone else (usually a family member) will be willing and able to sponsor you.

In our case, we had both been full-time students in the previous years, and as such we ended up just a bit short of meeting the requirements. We were required to ask a family member to sponsor us, and while they were happy to help, it is still an awkward position to be in.