The Level Zero StrategyThe most basic thing people do with Treasure Map is buy two as fast as they can, maybe get a third to help them collide, buy some treasures, and then use the golds off the collision to rumble in for Provinces.
This is a bad strategy. A really bad strategy.
In fact, the optimal play with Treasure Map and no other cards on board barely defeats not getting Maps at all. If this were all that was going on for a given board, then it really would come down to luck in if the Map player collides fast enough. (On the other hand, that's not really much different than straight Big Money, where it's all about how well that money clumps together).
Fortunately, there is almost always something better available on the board. And the big point here is that even when the Map player collides immediately, on the vast majority of boards, the other strategy is STILL going to beat this naive one. There is just so much else you can be doing, and four Golds is not really enough to finish the game out without support.
The Level One StrategyThe next step is to add in cards to help your Maps line up with consistency, greatly accelerating when they collide and give you the pay-off. The classical combos here are Haven, Warehouse, and Chapel (though to be fair, Chapel tends to help other things more). This is way stronger than the level zero strategy, and has enough raw power to be more or less correct on a non-trivial, if still small, number of boards.
Four golds probably still isn't enough, but a key point for this strategy is that the helper card helps you to smooth out later draws as well - this is the classical purpose of Haven, if you notice, and one of the main roles of sifters - at least in money-based or "good stuff" decks.
Still, this strategy tends to not be terribly strong, because though it has some punch, it isn't anything special - just a decent version of Big Money, and not even a great one.
The Best UsageAll this might lead you to think that Treasure Map just isn't a very good card and that you can pretty much ignore it. For the most part, you would be right. But there really are some cases in which it can be key. I am taking about cost-caring trash-for-benefit cards a la Salvager and most especially, Bishop. In this case, Maps are basically a way to use 2 buys and $8 to get 4 6-cost cards of value to trash.
In order for this to work, you need a very potent engine - you're gaining 4 golds with this every turn, and what's more, you're putting them on top of your deck. You need a lot of drawing power in order to break through all those stop cards. This tends to be pretty slow to set up. But if you can get it going, this really is a lot of fuel. For this reason, Bishop really is the best combination - the Golds provide you with a huge source of points to overcome even a big deficit of green cards, and the player who is trying to buy victory is probably going to stall, trying to grab them all.