Can I get a green card if I have married a US citizen but work in another state? How?

The short answer to your question is: yes, a U.S. citizen generally may petition for a foreign national spouse even if the two spouses do not work in the same state. The longer answer to your question includes an explanation that the USCIS can be expected to use a heightened level of scrutiny in such circumstances. The USCIS adjudicates each application on a case-by-case basis, and can be expected to require extensive documentary evidence explaining why the couple should be deemed to be living together in a bona fide marriage notwithstanding that the spouses work in separate states. After learning all of the relevant information about the two spouses, the employment situation and available documentation, an immigration attorney would be able to advise about the most appropriate documentary evidence to submit to the USCIS as evidence of the bona fide nature of the marriage - a key element for a successful adjustment of status application. Some immigration law firms, including mine, offer legal services on a "flat fee" basis so that a client will know the total expense from the very beginning, and a few immigration law firms, including mine, offer an initial consultation free of charge.