How often/hard should I do certain muscle exercises?

It all depends on you and what you like to do. You could do a full body workout about 3 times a week with a days rest in between each workout, so you can let your body rest and repair. If you work muscles to much then they wont get any bigger, an could possibly become smaller. You can work bigger muscles such as pectorals more often then smaller ones like biceps and triceps. Make sure that you are also eating the right food. :)