It's up to you. Always use a clean razor. There's no way to say how much you should shave, you can go totally "baby butt smooth" or you could leave the equivalent to a man's "5 o'clock shadow". It's all personal preference.
The above poster said it can itch/be painful. It can be. But the biggest thing people forget is to shave WITH the growth of hair's direction. That should help lessen the possibility of ingrown hairs. But there is no magic cure. When you shave your pubic hair always use a gentle soap or shave gel to help avoid razor burn. That's the mild burning, itching, etc.
As for arm hair, if you are talking like your forearm hair don't shave/wax etc!! It will come back darker thicker etc. the same way it does on your legs. You can look into bleaching it a lighter colour but be very careful with that it has pretty harsh chemicals. But if you are talking about your armpits, go for it. You will have to continue shaving though just like everything else you shave.
Hope this helped!
Personally I dont think it would be a good idea to shave your pubic hair because its really uncomfortable once the hair starts to grow back and painful. Plus it itches when it grows back and you get ingrown hairs sometimes as a result of shaving down there and those are painful. As for shaving your armpit hair I say go for it. I shave my armpits occassionally (sorry if that grosses you out) but its just cause it makes me really uncomfortable when I do shave cause then I get really itchy and then I itch so much it hurts. So I prefer not to shave very often. Regarding your arm hair I would HIGHLY suggest DO NOT shave or wax your arm hair. I say this because I shaved my arm hair when I was in grade school and it came back WORSE. The more I shaved it the stronger it would come back. I just wish I would have never shaved it. Unless you plan on regularly waxing I wouldnt suggest it. It also depends on your genetics some people after waxing for a while will stop growing hair where they get waxed or the hair will be thinner and less noticable. But then there are people whos hair comes back stronger. My dad has been plucking his unibrow for years and it still comes back full force. So I would definitely keep that in mind before you do that. Cause you dont know how your hair will grow back (better or worse) and plus if it is bad you cant take it back. Sorry if my reply is so long I just wanted to help out. I hope this helped you :)