I have mechanical disc brakes on my bike and if i look at the front one the left brake pad is hitting the rotor almost a cm before the right brake pad hits what should i do.

well you need to adjust the clearance of the pads, usually there is a little nob thign you rotate.

cm? a centimeter? If you have a mechanical brake, the pad operated by the cable will touch first and "push" the rotor into the other pad which does not move. They both can be adjusted for clearance, how depends on the brand. So, Hayes or Avid?

Yes thats right, usually the inner pad you need to take an allen wrench or something and move in a tiny bit and the outer pad you adjust by the nob. When i do this i like to have one playing cards clearance between pad and rotor

assuming the rotor is true a playing card distance would be just fine. Avid brakes look like the kind that the outer pad pushes against the inner pad that is fixed (non moving). It seems that mine however push a little too much, to the point that the rotor itself actually deforms a little until it contacts the inner pad. I dont know if this is damaging to the rotor and I have emailed Avid about the problem and havent heard back if this is okay. I will let you know what they say.