Best prevention for altitude related sickness/problems..........hydrate!
Drink water and lots of it. It will also give you something do when you stop every 5 minutes to catch your breath! You want to be in good condition, but you WILL be sucking air! Just a price us flatlanders pay. But it's not that bad, as with most things, moderation and sound judgement will mitigate the problems you will encounter.
Personally, I am prone to "altitude" headaches and I find if I "over hydrate" the problem is significantly reduced. Throw in some extra ibuprofen just in case. Works for me.