nothing will increase the size quickly. muscles take time to build. you have to be patient, and please don't get tempted by stuff like Xenadrine. Its dangerous. anything with ephedra or ma jong can cause heart problems. There are a couple of people out there waiting for heart transplants because they took that sh!t. the FDA is trying to ban this stuff. Its already banned in Canada and Europe. A great body on the outside isn't worth it if your methods cause problems on the inside.
Frankly, your best bet is to invest some cash in a personal trainer, and tell them what you want. I had a personal trainer for years, and it made a huge difference. As soon as I can afford it, I'm hiring him again.
Half the people in the gym are using the machines wrong. They don't adjust them properly, lift too quickly, or lift using the wrong amount of weight. A trainer can help you fix this. It's something you have to be shown in person by someone who knows (and someone who knows is not your buddy who's had a gym membership for six months. find someone who's trained in fitness to help you).
If you don't want to do that, your best rule of thumb is align the joint that's moving (ie. elbow on the bicep curl machine) with the axis on the machine. Lift enough so that it takes an effort to complete 15 reps, but not so much weight that you can't maintain proper form. Each rep should take at least six seconds...two seconds up, four seconds down. going slower is okay. going faster is not because you use your momentum instead of your muscles. rest for 1 minute between sets, and do 3 sets of 15 reps each.
make sure you add cardio training to your routine. a lot of guys dont' like to do cardio for some reason, but its essential for fat burning. there's no point in having great muscles if you've got a layer of fat over them so noone can see the definition of the muscles. start out at 20 minutes. find a elliptical machine that measures your heart rate, select the cardio program and go for it, following the directions. it will calculate a good heart rate for you. add one minute every time you go to the gym until you've worked up to an hour.
best of luck.