SGII tactics?

I played my first game of SGII a few days ago.	 Clearly, I have a lot
to learn about small-unit tactics.

I figured out one basic thing - don't let units become isolated!  Other
than that, I'm somewhat at a loss.  I come from an ancients/medievals
background, and the tactics for those periods are much different. 
Maneuver is more important, and missile fire less important than in the
type of combat presented in SGII.

How do you prevent games from becoming long-distance shooting matches? 
How do you introduce more mobility into the game without using vehicles?

What are good basic tactics?

I'd appreciate any advice or URLs for sites with good articles on this
type of information.  Thanks!