First Things First

If you want to ride the track you must consider your safety. The track can be dangerous, especially when you are trying to do new things - and that includes riding it for the first time. So, make sure you wear protective gear. At the very least wear a helmet plus long sleeves and trousers. Gloves are highly recommended. Arm and knee pads are a good idea too.

Now then, the first thing you'll need to do is practice riding round the track, slowly - but with enough speed to get up and over the jumps. You should aim to stand up on the pedals. You will never see anyone sitting down in a BMX race. If you're nervous, just try riding the top portion of the track for a while and build up your confidence before tackling the steep second berm.

Pumping

As your confidence grows, you'll want to increase your speed. So, first of all, try out this test. Sprint down the start slope then stop pedalling. See how far you get before the bike stops rolling.
Now learn your first technique and see how much difference it makes. The first technique is called pumping and it's mainly about keeping it smooth. As your front wheel rolls over the top of a jump, pump (push) the handlebars down the slope. Also continue to pedal hard if you can. Pumping the jumps is an essential skill and will increase your speed. It will also give you more control through difficult doubles because you will keep your front wheel on the ground. If you don't pump, the front wheel can lift over the first jump and smash into the second, wiping out your speed and possibly making you lose control.
Once you've got the hang of it, try the test again - sprint down the start slope, stop pedalling, pump every jump and see how far you get before the bike stops rolling. I'll bet you get further than before. If not, you're not pumping hard enough. Keep practicing.

Manualling

The second technique to develop is more advanced - it's called manualling. This involves riding the bike on the back wheel without pedalling! It's another technique which increases smoothness though the jumps. As you ride over the first jump of a double, you need to bring the front wheel up. This is achieved by pushing the pedals forwards, partially straightening you legs, and getting your ass back behind the bike. Control your balance by shifting your hips/weight backwards or forwards. Find a double wich is not too large and practice on it. The first double on the first staight is a good one to start practising on. Then you can move on to the doubles on the second straight. Manualling is a difficult skill to learn, so don't get dis-heartened if you can't manage it straight away. It's also much harder to do if your bike is a bit too large for you. Try to practice on a small bike. It's also a skill you can practice away from the track. Remember, as with all these BMX skills, you'll only get better if you practice.....and practice......and practice.