The best decision to make is not to fly. If you find yourself in the unfortunate situation where you need to deploy your reserve, do it and don't hesitate.
L - P/T - R - A - D - PLF
As with everything that is important to remember, mnemonic devices are great.
LPT RAD PLF is a good one, or LP TRAD PLF. Choose one and stick with it.
LOOK
PULL/THROW
RETRIEVE
AVOID
DISABLE
PLF
If you are landing in trees, you can protect your face and avoid having branches catch the under side of your chin guard by placing your thumbs under your chin and covering your face with your hands and fingers. If you land in water try not to move your legs too much. They can become tangled in the lines which will tend to sink. The back protection in your harness may try and float you face down, so get one arm out of the shoulder straps and reach around to hold the harness. This will keep your head out of the water while you finish unbuckling. If a boat is coming for you, stay still, and away from your lines, using the harness to keep you afloat. If you’re in moving water, and are worried about becoming tangled, leave your gear and get to shore. If you try to fight your gear in water it can drag you under. If you land in power lines DO NOT touch the ground, the Kevlar lines can conduct electricity. Have someone call the authorities and wait for help. If it’s windy, and you can’t get free of your harness, you will have to cut the reserve bridle(s), wing risers, and speed-bar lines with your hook knife. After landing under reserve, if you are not hurt, quickly get up and gather your equipment. This signals to others that you are OK. If you suspect that you are injured, don’t move, and wait for help to arrive. After a successful reserve deployment it is customary to send the person who packed it a thank you!