You probably have not been using your front brake enough. Did some hard decelerations on a quiet road. Get up to 40 or 50 then brake firmly with the front brake several times. Don't come to a full stop, don't want heat warpage.
If this doesn't fix it, then you can follow this procedure.
Do your disk brakes squeal, they all do to a certain degree but can be worse if the pads and disk are glazed, usually the result of frequent low pressure use of the brakes.
Her's one cheap way of fixing the problem
First, you'll need these supplies:
#60 grit black sandpaper.
Medium grit ScotchBrite pad.
Acetone or Brake cleaner.
1) Unbolt the brake caliper and remove the disc brake pads.
2) Get some coarse #60 grit black sandpaper.
3) Lay the paper down on a VERY flat surface. A sheet of glass, a piece of sheet metal or other really flat surface.
4) Take one brake pad, put it compound side down on the sandpaper, and sand the surface till it looks fresh and new. Use a figure 8 motion while sanding, and be careful to sand the pad evenly. Then do this to the other pad.
5) Get some acetone or brake cleaner to clean the surface of the disc. It needs to be a grease-less cleaner that will leave the surface of the disc clean and completely dry. Paint thinner or cleaning solvent are NOT good for this! Take a clean, lint free rag and apply the acetone or brake cleaner to it, and wipe both sides of the swept area of the disc, (the un-painted area that the brake pads rub against), to remove any oils and crap that have accumulated.
6) Then take a piece of the #60 grit sandpaper and carefully and lightly sand both sides of the disc on the swept areas until you can see that you have removed the surface glazing from the disc. You can tell this by the sanding scratches appearing on the disc surface.
7) Then use the ScotchBrite pad, the medium grit is best, and scuff the swept area of the disc until the sanding marks JUST start to disappear. Use compressed air to blow all the abrasive debris off the disc, or, alternatively, use a shop vac.
8.) Clean the disc off again with the acetone or brake cleaner and then re-assemble the brake caliper and re-attach it to the fork leg.
9) Before you ride your bike, be sure to pump your brakes a few times to get the hydraulic pressure back up and to seat the pads. Then go out for a ride and use the brake lightly just to confirm they are working correctly. Then, as you are riding in second gear, about 25 miles an hour, lightly drag your front brake a couple of times for about 5 seconds each time. That's it, you should have vastly improved braking and a quiet operating disc brake.
Note: This procedure applies to the OEM pads. If you are using sintered metal pads or kevlar based pads there is a different procedure to break these pads in.