The best size and color will vary depending on the location.... depth, water clarity, and forarge in that specific water. One thing I have always had good luck with is to give them lots of action by popping and jerking them. But my personal favorites are rainbow, black and gold, black and silver, the newer brown trout, and perch. in the fall, fire tiger works too. #5's on 6 or 8 test seem to be about the right weight for casting
For a more realistic presentation in super clear water take off the treble hooks and replace with a single. Also make sure the lure is tuned. sometimes they pull a little right or left. you can change this by tweeking the eyelet a little bit, dont push on it to hard or it will crack the nose of the lure. the "rapala knot" is also good to use because it allows the lure to wiggle a little better than using a standard clinch knot.
Also the "countdown" effect works well to judge how deep the lure is sinking. Rule of thumb is about a foot per second. you can test this by watching the lure sink. If the fish are feeding in a certian zone, let the lure sink and count the seconds so you will know how deep you are fishing the lure.
At $7.00 a pop for a rapala, I have found myself using primarily maribue jigs for trout instead of rapala's, I can tie jigs for about $.20 a peice and find them more effective in most trout waters than minnow plugs when fished properly.