Hey Deck, don’t take this the wrong way, but I managed a shop for 7 1/2 years and whenever someone came in saying “I was just working on my bike at home…”, you knew it meant an extra $20-$50 in labour if not more. Now I am not telling you that working on your own bike is a no-no. In fact most riders, especially triathletes, should know more about their bike so they understand the hows and whys of their bike setup. However, TAKE A CLASS! Most LBDs offer some sort of home mechanic’s class tailored to different abilities and knowledge levels. This will help you avoid making the basic, easily avoidable mistakes.
It is funny that you should mention the cassette lockring as this is one of the places where you most frequently see the home mechanic mess things up, sometimes in dramatic fashion. The most common mistake the home mechanic makes is over torqueing bolts, lock rings, etc. There is an actual torque specification stamped on the Shimano lock ring, but realistically, almost no one uses a torque wrench on the lock ring. A simple rule of thumb is tighten the lockring until the “teeth” engage on the knurled surface of the smallest cog and then give it another 3/4 to full turn, max. Any more than that is unnecessary to keep the cassette in place and will make it very difficult to remove the lockring in the future. And make sure grease the threads, do NOT use Locktite as one brainiac who came to the shop did.
As for getting the wheel back on easily, if you are riding a bike that has vertical rear drop outs, put the chain in the smallest cog/smallest chain ring combo. This takes all the tension off the chain. Open the brake then grab the top of the wheel with your right hand so that it does not fall out of the frame and go crashing to the floor when you open the QR lever with your left hand (your QR levers should always be on the left hand, non-drive side of your bike). Now switch hands, grab the wheel with your left hand as you push the bottom of the rear derailleur towards the front of the bike. Push the derailleur by pressing your thumb on the little tab that covers the lower pulley. Push the derailleur until it is almost perpendicular with the ground. This will move the rear derailleur out of the way as you push the wheel down and out of the frame.
When you put the wheel back in the frame, make sure again that you are in the small/small combination. This way you will know which cog to line the chain up on when you reinsert the wheel. Again push the derailleur forward with your thumb and slide the wheel home into the drop outs. Close the QR, take the bike out of the stand and put both wheels down on the ground. Now open the rear QR lever, you will probably feel the wheel settle into the drop outs and centre itself in the frame, then simply close the QR and voila, your wheel is installed and centered. If you are using a frame with horizontal drop outs, rear wheel removal and reinstallation is always going to be more difficult. BTW, opening and closing the QR with the bike on the ground also works for assuring your front wheel in properly seated and centered (assuming that your wheel is properly dished/trued and that your frame is not out of alignment).
Make sure you remember to close your brake caliper after reinserting the wheel. If your brake is not centered after wheel reinstallation and centering, it is likely because you knocked the brake caliper askew when removing the wheel. You should be able to simply twist the brake caliper back into place so that it is centered around the wheel. If you cannot easily twist the brake caliper, then the bolt holding the caliper in place is too tight. You can also use the 2mm set screw on the side of the brake. Turning the set screw clockwise pushes the caliper away from that side of the rim and pulls the opposite brake pad towards the rim. Turning it counter clockwise does the reverse. Hope this info helps!