There's an intersting thread over on BGG called "I Want to be a Wargamer" about how new wargamers can get over the hump of learing how to think strategically and tactically while they are starting to play.
There's alot of excellent advice, but I think one the absolutely best books I've ever read as an introduction to tactical thinking is The Defense of Duffer's Drift .
It has the virtue have having tremendous insight with the added benefit of being very entertianling presented.
As the US Army Command and General Staff College notes: A classic in small unit tactics in the British and U.S. Army, this book is recommended, without qualification, for the modern professional soldier.
What would you do? Lieutenant Backsight Forethought (BF to his friends) has been left in command of a 50-man reinforced platoon to hold Dufffer's Drift, the only ford on the Silliassvogel River available to wheeled traffic. Here is his chance for fame and glory. He has passed his officer courses and special qualifications. "Now if they had given me a job," says like fighting the Battle of Waterloo, of Gettysburg, or Bull Run, I knew all about that, as I had crammed it up...."While BF's task appears simple enough the Boer enemy causes a multitude of problems, but you, astute reader, with a sharp mind and quick intellect, will no doubt, solve the problem before the first shot is fired.
Here is an illustration from this 1905 classic.
When I was a battery commander and my new First Sergeant wanted advice on how to set up the battery defenses I recommended this book. It's not the specific advice, of course, that is important, but the way that it helps the reader develop the critical thinking skills and tactical sense to deal with his particular tactical problem.
I can't recommend this too highly.