First, a matter of safety (not yours, the reeds'). For reasons best known to themselves, reeds seem to enjoy falling out of drones. In the days of cane reeds, this was not a disaster. You cold simply shake the offending reed out through the drone stock, wipe off whatever disgusting substances it had picked up in the bottom of your bag, reinstall it, and go on your way rejoicing.
Not so any more. The toungues on artificial reed are thin strips of plastic, and they protrude just enough to snag on the stock when you try to recover them. A bit of a nudge will kink the tongue beyond repair, and you're out of business until you get the tongue replaced.
Fortunately, there's a simple solution to this problem. Take a short piece of (preferably waxed) yellow hemp, and tie it snugly around the bottom of the hemp on the reed. Leave about two inches of tails dangling from the reed. Bring these up across the hemp on your drone, so that they get trapped between the drone and the stock. When your reed decides to go exploring, its progress will be halted by the noose. Just point the drone downward and remove it, and the reed will follow it out of the stock with no damage to anything but your dignity.
To me, the most important point in adjusting reeds is to make my pipes easy to blow. I find that I play better if my eyes aren't bugged out to the point where they knock my glasses off with the effort of blowing.
Most reeds, as they come from the manufacturer, are set up stronger than they need to be. The reason for that is that he doesn't know how strong your chanter reed will be, and he wants the reed to work right away in your pipes. Making it efficient is left up to you.
The fiirst order of business is to break the reeds in. Yes, just like cane reeds, it takes a few hours of playing to make the reed understand what it's supposed to do, and get it settled into its routine. Unless it's taking a huge effort, it's probably best to leave it at the factory setting until you've played it for a few hours.
Now you can set the reeds up. My routine for this is to nudge the bridles down toward the open end of the toungue until all of the reeds cut out when I strike in the chanter. Go slowly; if you can see how much you moved the bridle, it's too much.
This will certainly make your pipes easier to blow, but it doesn't give exactly the effect you want. Now comes the fun part; getting the reeds to work with a minimum of effort. Starting with one of the tenors, edge the bridle up ever so slightly (no, not that much) and try it. Make sure that it moved evenly all the way around, not just over the tongue. With any luck, the drone will keep going while you play a couple of tunes. If not, try again until it does.
Now do the same thing with the second tenor,and then with the bass. At some point you may find that the first tenor starts to cut out, because it's no longer getting the same share of the air. Go back and readjust it; this is a sort of balancing act.
With all of the reeds working, you're ready fo the final test. Get everything going nicely, then clamp down hard on the bag with your arm. If all of the drones cut out together, you know that they're set up to work as efficiently as possible.
Some Hints on Learning Tunes
Some Notes on Drone Reeds
What it takes to learn piping
The tunes
Building your Band's Repertoire