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...
There's no distinct crest marker, so you just need to aim at the top of the helm.
Don't waste boosts just because you've got them. They don't disappear.
Upgrade your armour whenever you can, for things get tough pretty fast.