| Speaking from the experience of having one save my life. Get a full-face helmet. Half helmets will only protect the top half of your head, which is kinda useless if you land on your side.
If you get a full-faced, you can get them with vents that you can open or close according to the weather. Keeps you cool in the summer, and well.. warm in the rain. Make sure you buy a new helmet, and not a second hand one either. The instant that a helmet is damaged by any sort of impact, no matter how remote, micro-fractures in the shell will form, and it effectively becomes almost-useless as protection.
One more piece of advice.. wear glasses of some sort.. sunglasses or regular ones.. in case your visor pops off, your eyes will still be protected.
LAST piece of advice.. I promise... get a good suit.. preferably one with kevlar padding.. it'll cost an arm and a leg.. but it might save an arm and a leg at some point too. The only reason my left leg is attached and I didn't lose more than one internal organ was due to an inch of padding all around.
Hope this is helpful. =) | 
