How do I get my hydraulic disc brakes working well again I just bought a new bike (my first brand new one ever) a few months ago and a while ago I decided to give it a wash and after that my front hydraulic brake hasn't been working as strong as it used too. I used to be able to lock it up on gravel with two fingers, now I can't get them to lock up at all even with all my strength.

(This is my bike) http://www.trekbikes.com/au/en/bikes/mountain/sport/3_series/3900_disc/
Most likely cause if the disc and pads are contaminated. What did you wash it with? Many cleaners leave a residue. 

Worst case the pads need replacing. The discs should be well cleaned before installing new pads - Use a solvent such as brake cleaner, methylated spirits or Isoprop alcohol, and rub the discs to be certain no contamination is left on them. 

Best case is a good clean of the discs solves the problem. If this does not work, remove the pads and clean with cleaner and re install and clean disk again. If this does not work there are tricks with pads such as burning, sanding etc that might help - I won't cover how to do it here as its well covered elsewhere. 

How far you go trying to restore contaminated pads is more a matter of how much time and effort is needed vs cost. Eventually (and quite early for me) patience runs out and as new pads are the guaranteed fix, its down to the LBS I go.