I generally try the start position out for a while, to see if there are greener pastures a little further out. My last game, I played as the Japanese on a medium pangea, and wound up on a peninsula. I thought it was a bad spot, but I was able to block it off, expand south to box in the Zulu and Indians, then settle the north part of the peninsula at my liesure. Made a very nice defendable location, as I was able to fortress my border later and secure it with infantry. The only approach for my enemies was by sea or through my "great wall" of infantry. The wars I waged were with far off civs, using ROP and railroads to get to the front, so my homeland was never threatened except in the early ages.
My current game with the Persians had me in the middle of tons of forest and jungle. I stuck it out, and now have tech and power leads. I am on a continent, and share my borders with three civs, with an inland lake blocking the Zulus from immediate access. I have an army of workers clearing jungle and forest, and I anticipate a domination victory.
Funny thing about that one, six of the civs (including mine) are on the main, huge land mass, and the the AI put the Germans and the French on a little continent, and they are VERY backwater (ten cities apiece, maximum). I am the only civ to have contacted them, and they live off of my tech offerings. I make sure they are equal to each other, so they wont go destroying each other just yet. Once I get riflemen, they will still be in the early middle ages, and they will be my unwitting slaves.
