I use a lot of tactics.
Especially on Tom Clancys: Endwar
My main one however is the imple surround/outflank manouver.
I will send small groups (always made up of some engineers, some APCs and some tanks) in different directions, down different tracks to capture objectives, and in the end surround the last objective.
It works most of the time.
Another good tactic is boxing the enemy in.
Just send some large groups of heavy armour to block the tracks and roads out of the enemy bases and then send other units to casually stroll around and capture the objectives, while you prevent the enemy from leaving the dropzone. The really good tacticians, wait till they see a deployment helicopter and then call in an airstrike on it while its unloading its troops.
I love strategy games