How do I get my biceps big properly?

[-paradox-]

Oh man.. Don't just do your biceps. Your triceps make up 3/4's of your arm. If you're going to work out do it right. Especially since you have a gym membership. Do something like this

• Monday -
  --------- Chest 12-14 sets. 8-10 reps max on each set.
  --------------- Bench 4 sets, incline bench 4 sets, flies 3 sets, crossover machine "flies" 3 sets
  --------- Bicep 12 sets. 8-10 rep max on each set.
  --------------- Hammer Curls 3 sets**, Preacher Curls**, Bicep Curls, Crossover machine preacher curls.
  Tuesday -
  --------- Tricep 12 sets. 8-10 reps max on each set.
  --------------- 3 sets Tricep pull downs, 3 sets tricep extensions, 3 sets tricep pulls, 3 sets tricep dips.
  --------- Shoulders 12 sets. 8-10 reps max on each set.
  --------------- 3 sets Front raises, 3 sets side raises, 3 sets arnolds, 3 sets military press.
  Wednesday -
  --------- Back 12-14 sets. 8-10 reps max on each set.
  --------------- 4 sets far grip pulldowns*, 4 sets rows, 3 sets "lawnmowers", 3 sets deadlifts
  --------- Core
  --------------- 3 sets sit ups, 3 sets leg raises, 3 sets bicycles, 3 sets in and outs, 3 sets hanging leg raises
  Thursday -
  --------- "Rest day"
  ----------- I do leg workouts on rest days. You can actually take off today.
  Friday -
  Start all over again!
  

Feel free to throw core workouts in every other 2 days or so. Work your lower back as well, if you work the front of your core be sure to work the back.
If you are working your chest be sure to work your back as well. If you don't it can cause back problems because your chest is too strong for your back and it makes you hunch over.
As for forearms, throw those in every 3 days or so as well.

** For these bicep exercises, the hammer curl is good for your forearms and lower bicep. DO NOT EVER PUT MORE WEIGHT THAN YOU CAN DO. If you can only do 20's properly do 20's. Do not put on more weight and lose form. If you lose form and only work the top of your bicep because you're not extending your arms all the way out you will have little top biceps and a gap between your elbow and bicep. It looks funny. So form over weight.
The preacher curls are also very good for lower bicep.

* The pulldowns can be pull ups. It depends on how strong you are. These are hard to do 8-10 times for most people. Chins ups are easy, wide grip pull ups are hard.

Good luck.
Drink your protein and a lot of it.