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...
Increase the distance your melee weapons can reach as soon as you can.
You get more for melee kills, so make sure you keep running.
You want to be in front of the scientist at all times, clearing a path.