The most important strategy in these games is to save, save, and save again. Save when you are going into an area that you feel is a trap. Save before performing a complex set of maneuvers. Save before entering an area that you know is filled with guys. Saving is the most important strategy that I know of.
Another strategy,
especially in TR2, is resource management. When they give you the
grenade launcher, don't waste the ammo on the first guys you
meet. Save it. A more important resource that is difficult to
find are health packs. In TR1, health packs were abundant. But
not in TR2. Save every one you get, because you are going to need
them.
My third and final strategy is be alert. If something looks like a trap, it probably is. If an area is highly gaurded, or sparsely lit, then chances are that there is something important there, like a weapon, a key, or a secret. Be creative and explore the world, but be cautious.