Try this, It really worked for me and makes sense, I wrote my entire training program down if you want to check it out but here's how I got started.
Take Bench Press: Warm up with at least two warm up sets of 20 reps
Then Max out with something close to or using your 1 rep max.
Have a spotter help you to get 3 more reps in that same set. So you're doing say 80kg x 4 = set 1 with your spotter keeping the weight moving on the way up, and you controlling it on the way down.
Then do say 50-55kg or something that you can do 4 times on your own, and have your spotter get you 2 more. So 6 reps = set 2
THEN do a weight that you can get 8-10 on your own and have your spotter get you 1-2 more.
This works because you are overloading your muscles and forcing them to adapt and grow. Just make sure that you're warmed up before doing it. AND make sure that your spotter is keeping the bar moving. You should never be straining with the bar stuck at any spot through the lift. That leads to over fatigue of the muscles and you will get burnt out.
That was STEP 1.
STEP 2 is to eat eat eat eat eat!!! Make sure you're consuming at least your Projected Weight in Grams of Protien. A shake in the morning as soon as you wake up and one right after you work out.
As for sets, after 2 warm up sets, 3 sets for 3 exersizes.
I'm on weight gain now and have added a bit over 10kgs since around xmas time. Here's what I recommend...
Do 3 exercises per muscle and 2-3 sets per exercise. You only need to do 3-8 reps per set.
Do your warm up then get straight into a heavy set. In your 2nd and 3rd set you should only be able to get to about 3-5 reps by yourself - always get a spotter to help you on the last couple of reps to take you up to 5-7. These last 2 reps are the most important because these are the ones that will make you grow.
This is a good workout, but I believe diet is considerably more important to gaining muscle mass than what you do in the gym.