I've tried various methods, but a little notebook seemed to always work the best. Of course you can always transfer some data to a spreadsheet if you want a chart or something, but the only thing I really ever check is "the last time I did this exercise for this target reps what weight did I use and how many did I get?" Use that number to determine what to do today. Checking takes about 20 seconds. I now have years of weight training workouts in my little notebooks :)
