When people first decide to lift weights, they usually want to get bigger biceps. Here are some tips to increase the size of your biceps and the weight they can lift!

Progression
Try to keep increasing the weight you lift each week, without compromising form. Your body will constantly adapt to increasing loads, i.e. your muscles will grow bigger if you constantly increase the load being placed on them. Lifting the same amount of weight week in week out will mean that you wont be getting much bigger or stronger.

Switch it up
In a similar vein to progression, constantly keep your body guessing, keeping it from getting stuck in a rut. Change the exercises you do every few weeks, vary the angles from which you train your muscles. If you do barbell curls every week, try ez curls for a few weeks. If you do standing curls, try preacher curls for a few weeks.

Form
Don't cheat, you are only cheating yourself. When curling, extend your arms nearly all the way, don't bounce or rock your body to help lift the weight, keep the rest of your body still. Don't rush lifts, slowly lower and raise the weight. On a bicep curl, don't raise the barbell all the way to the top, as the top of the lift gives you chance to rest when you should be keeping your biceps under constant load.

Don't over train
One targeted workout per week is enough for your biceps. They are a relatively small muscle, and are also trained along with compound movements for other exercises on different days.
Muscles grow when at rest, not during training. Over training will have the opposite to the desired effect.

Eat
Your body needs enough nutrients to repair the muscle tissue you have trained. You must aim for 1.5-2g of protein per kg of bodyweight per day.