What it shakes are the handle bars steady but the wheels shaking or does the shaking front end make the bars wobble too?
There are about 1000 things that could cause this problem and you should make sure you figure it out before you do too much agressive riding.
First jack up the front and slowly rotate one front tire. Use a tape measure or ruler to measure from the rim to the frame and see if either of the front rims are bent.
While it's up, from the side of the quad grab the top of the tire and the bottom and slowly push the top of the tire toward the frame and then pull on the top of the tire and push in on the bottom of the tire. Listen and look for any play. This will take some close attention because the A arms at the frame, the ball joints, and the wheel bearings will all be effected by this test. You may also notice play in the lower and upper shock mounts. ANY play should be noted. If there is play in the wheel bearing, tighten that bearing up a little and see if it improves. If there is play in the A arms or ball joints, you will need new A arm bushings/ or bearings {I sell bearings for this application if you need them and give HQ members a discount}. If your ball joints are bad, you need new A arms. There is no way to service the stock ball joints.
While you have it up, grab the tire and the tie rod and see if there is any play in the tie rod end. Also look at the bottom of the steering stem where it meet the frame and move it by hand left to right to see if there is any play there.
Put it back down and put your foot next to the tire and slowly move the handle bars as if you are trying to turn. Your foot will prevent the bike from turning. Now look again at the tie rod ends, the steering stem lower pivot point and the top of the stem by the bars {you may want to remove the radiator plastic to see this in clear view}.
Push down on the front sharply and listen for clunking noises you can also lift up sharply on the front and listen for noises that would indicate sloppy suspension.
It is important that your front suspension be in excellent condition at all times. Loose steering results in loss of control and what's worse is losing a ball joint or tie rod and really biting it
You may also have a bent rear axle or extra loose rear suspention but that is less ikely than the front.