I don't think you can go too wrong with your Halloween outfit, even the standard white bedsheet with holes on it can be a pretty scary look if you do it right.
But there's been a recent string of costumes that have made news headlines for being offensive or inappropriate, and are probably the ones to avoid in my opinion.
So this halloween, keep it clean (shaven)... And avoid wearing anything that looks like you might have an explosive device strapped to you (especially if you plan to use public transport).
Keeping it political, the next type of costume I'd recommend you avoid is anything to do with the Nazi party.
As, Prince Harry of England once found out - people don't take kindly to swastikas - so make sure your halloween outfit doesn't have one!