The best training is learn by doing. First of all, make sure you are using saltwater reels. Freshwater reels will never last no matter how well you clean them.
Most reels you buy come with a manual and/or parts list.
What I do is lay out some newspaper, As you take off a part, just lay it on the paper in a row. Once you get the reel broke down as far as you want, start cleaning. I use a rag, a nylon toothbrush and some Q tips. Wipe away all the old grease and dirt. Clean one part at a time as you put the reel back together, as to not mix up parts. Grease for gears, oil for bearings.
Just take your time, and remember that too much lube is a bad thing.