One potty training book I read blase'ly passed over this issue with, "well, underpants are easy to wash and he'll take a bath in the evening anyhow" ... OY.
I taught my kids a pretty structured way of toilet-papering from day one, because I had a girl first and there is the whole make-sure-no-poop-goes-forward-during-wiping (so no nasty infections happen) problem. Perhaps why girls are born with hymens--did I just discover the evolutionary reason for that?!? weird.
Anyhow, my son particularly likes things that have structure and a "right way" to do them, and as far as his hygiene goes, he is pretty self-driven. So I taught him, like his sisters, how much toilet paper to use (no longer than his arm), how to unroll it, how to hold the top with his left hand so he could pull the bottom and rip it off with his right hand, how to crumple it (loosely!, instead of into a tight useless wad), and the mechanics of how to wipe, guiding his hand to make sure he understood how far down to reach and talking to him about "how hard does Mommy have to wipe to get your butt clean? alright, so you need to wipe that hard too, then" ... and then he needs to check the toilet paper before he drops it in the toilet, and if it isn't clean, he needs to do the whole thing again. When he was still young enough that I was supervising the situation (3), it usually took three wipes. His underpants have rarely had any stains in them ...
That said, one of my daughters, also trained when she was three, has for reasons unknown suddenly forgotten that toilet paper exists for peeing ... luckily she's a fairly tidy pee-er, but ?!? where did the two years of habit go???
Anyhow, it sounds like from the other responses maybe my kids were outliers on the early-effective-wiping scale, but I figured my 'method' might be useful to someone ...