Strategy is quite different from tactics. Sipmlified, here's how I understand it:
A strategy is PLAN that you make before the outset of the conflict. It's a plan that you will try to stick to, because if everything happens according to your strategy then you expect it to go well.
A tactic is a somewhat reusable course of action that has no specific context. You use a tactic within the scope of your strategy. A tactic is an action or set of actions that you perform during a conflict when a means to fullfiling your strategy becomes more likey to succeed than you had thought before. Use moose's link, Sun Tzu is badass (I've read his book, UberNerd).
I said I wouldn't, but you need help. Oh and, yes, I'll browse Tremstats to look up any player who I'm seeing with any regularity. I usually don't remember much more than their total hours played, and human play/alien play ratio.
*1* So it's a small game and I'm on aliens. 3 humans join. One is "><Warlock", one is "-sg-aequitas", and one is "arnold". Based on what I don't know about arnold (from tremstats), I assume that he is new, and I formulate the strategy that when I rush the human base, I will dretch HIM. It will be easy to know which he is because new players are allways looking in circles, or walking to odd places in the map.
Another example:
*2* I notice that KiLL3R (fictional) joins. I'm thinking of going alien builder, but I suddenly remember that on his kill-graph, there is a large green spike right near the beginning. This lets me know that KiLL3R likes to rush, and that I shouldn't rebuild the Overmind and pray that he trips on acid. So I make the tactical decision to evolve and dretch him.
Sheesh.