Undo the bolts that hold the caliper to the bracket a couple of turns, spin the wheel and pull the brake to stop the wheel then, holding the brake on, carefully tighten the bolts alternately. A lot of people tighten one bolt right up which then twists the caliper and they still drag afterwards. Tighten each one alternately and a bit at a time until they're both fully tight.
Avid Elixirs are simple enough to keep working perfectly (Juicys, particuularly the Threes, are lousy - the pistons stick). First, you have to remember that they're a closed system, so air in the system stays in the system. You're best bleeding them with the bleed kit and brand new DOT5.1 fluid from a newly opened bottle, but slightly older fluid is OK if you lock off the syringe and pull the plunger to get the bubbles to accumulate on the walls of the tube. I buy little bottles of 5.1 from Halfords and I bin fluid that's over 3 months old.
The bleed method in the Avid manual is rubbish - use the one on the Park Tool site. But I also tap the tubes to make air bubbles move up as I syringe fluid through the system.
A couple of things I've found:
If the pads are miles from the disc when you bleed them, they will pull back from the rotor and give you too much lever travel before they bite. Removing the wheel and pulling the lever gently so that the pistons extend (but not too much, or the rotor won't go back in between the pads) sorts this. You need the pads to be closer together than the thickness of the rotor when pulled and to extend back so that you can get the rotor in. If you overdo it, gently push the pads apart with a big screwdriver or the Avid red pad separator thingy.
(This applies to other makes of brake, too) If you're out on a ride and the lever is coming back to the bar, you can get them to self bleed by leaning the bike so that the hose points directly down from the lever then flick the lever. This allows the air in the pipe to travel up and trough the small top up hole inside the lever reservoir. If you're doing this to the back brake and it isn't working, stand the bike on its back wheel and bounce it up and down to move bubbles up the pipe then try again.
I hope this helps.