Most often I play with conditions poised in the middle. Medium temperature and humidity; 4 billion years.
More mountains means it's harder to build mines and roads, but hey, if you're Industrious that is not a problem.
Again, more jungles means extra hard work clearing them, because those squares are no good until cleared.
More mountains means more chance of iron, gold, and gems. More jungle means more chance of coal.
I never choose islands. I like either pangaea or big continents, max land area.
I most often play on a large map. I take the full dose of rivals, always random. (But they're not completely random; Persia always, ALWAYS gets Babylon as a neighbor.)
I hate, hate, HATE having to start on not a river. If on the first move I'm not on a river, I usually ditch that game and restart. If I have to move one square to get to a river, thereby wasting my first 4000 BC move instead of building a capital, it puts me at a severe disadvantage from the get go. The other civs are merrily founding new cities like crazy and I never get caught up until late in the game. I have won games like this, by Space Race, but am always way behind on points until the modern age.
I wish I could tweak the game so that I can always start 4000 BC on a riverside seacoast square. If I don't get a river at the start, it almost isn't worth it to continue. (Even though I have won games with this disadvantage.)