Update: I was unfortunately not aware of Shamus Young's severe criticism of Fallout 3 available here to link in the original piece and I regret that. It dovetails rather nicely with what I've written and it's much better executed than my piece. I strongly recommend anyone...
Keep on the move and your shots will go farther across the battlefield if you do.
Don't waste your beam. And make sure you turn it off between rounds.
The jump function can save your life if you use it at the right time.