With hydros, the best way is to loosen the bolts squeez the lever and zip tie it down so the pads stay closed aginst the rotor.
Then check to see if you need any shims between the caliper and the mounts on the fork or chain stays.
If it is not flush aginst the mounts go to your lbs and get some shims. They come in .2mm and .5mm. get a few of each. Then add then one at a time until you get a tight fit and then torque the bolts down. release the lever and you should be good to go.
With new discs there will always be some drag until the pads start to wear down.
