Sentence 1) is wrong. Seit + verb indicates continous tense. You can say: Ich lebe seit langer Zeit in den USA. - I have been living in the U. S. for a long time. Ich lebe seit 2010 in den USA. - I have been living in the U. S. since 2010. Sentence 2) is close to perfect, just the word order doesn't sound quite natural. Ich habe für eine lange Zeit in den USA gelebt. - I have lived in the U. S. for a long time. The usual word order in German is TeKaMoLo - that comes from Latin and is short for Temporal, Kausal, Modal, Local = time, cause, manner, place. Sometimes it is also acronymed TeMPo (time, manner, place). Of course not each and every sentence contains TeKaMoLo and sometimes the word order can be changed to stress on a certain information but for a learner it gives a good orientation until you get the right feeling for the correct word order.