How do I prevent the Hydraulic Disc Brakes on my bike from rubbing? I recently bought a new Polygon Strada 5.0 mountain bike with Shimano BR-M355 hydraulic disc brakes and have had issues with the brakes rubbing. I fixed the rub but now it is happening again. 

The fixing process takes time and I'm asking if there are any suggestions/ideas on how to prevent this from happening again.
Likely the brake caliper assembly isn't mounted quite parallel to the rotor and needs to be slightly adjusted. This is a pretty easy process that takes less then a minute to complete:


Using a 5mm Allen Key, slightly loosen but do not remove the two
caliper fixing bolts so you can move the caliper assembly
side to side.
Depress the brake lever so the rotor is being clamped by the pads
and then re-tighten the caliper fixing bolts to 6.0 - 8.0 N.m (53.0 - 69 in. lbs.)


If you ever need to remove the caliper assembly from the mounts (for instance to change your brake pads) you'll use a similar process to re-align the assembly to the rotor. In that case you would re-install the caliper assembly but only screw the caliper fixing bolts in part of the way and then follow step #2 above.