If you're looking for a simple overview of different tactics that have been used then the
Wikipedia List of Military Tactics is a good place to start reading. Not everything is still in use, obviously, and some of the pages are rather brief on the specifics of different tactics, but it's a good place to start. For a more bit abstract view of the topic, I suggest you check out the
Marine Corp's Tactics manual, which covers a lot of the exact reasoning behind tactics (if not the exact maneuvers in detail). For more specifics on exact maneuvers you probably want to check out various military manuals, such as this
Marine Rifle Squad Field Manual, this
Army Infantry Rifle Platoon and Squad Field Manual, or this
Manual for Marine Military Operations on Urbanized Terrain. A lot of it won't necessarily be applicable to what exactly you are trying to learn, being probably
too specific for the generalities you are looking for, but if you want specifics they're the place to go, and you can find quite a few more that have actually been published by the military at places like
this.
Beyond that the basic ideas of studying warfare pretty much involve looking at scenario after scenario that have been performed in the past (history, yay!) and seeing what they did that worked and what they did that didn't. To quote the earlier linked Tactics manual from the Marines:
The leader's skill is essentially one of pattern recognition, the ability, after only seeing a few pieces of the puzzle, to fill in the rest of the picture completely.
If you are really interested and have access to a library you might also want to see about reading as many of the books on
this list (note: it's a .doc download link, so don't freak out) as you feel necessary; it's the current list of the top 100 books for West Point Officers in training to read, and includes many a book on both tactics and strategies in use throughout both history and today.