I have them roll paper around thir hand, and then use their hand like tongs, so thumb is designed to just hold the paper in place.
I tell them to wipe, and then do that 2 more times.
If you need a kid to wipe more than 3 times, maybe they had bad food or are sick. Not ever been a problem with my kids if they wipe 3 times. Ever...Though, I get "skid marks" when they are trying to go without a wipe hurrying back to a game or whatever.
If at all poossible, keep them naked for about a week or two as much as possible, so you and they can see the action when it comes. Problems with modern diapers is they wick away moisture, and keep them too comfortable to learn.
Tie tons of praise to the act of "Poopin' on the Potty" (we have a little song and dance we do every time there's success...I have 3 kids under 4 years old).
Also try to have kids a little older (8-15 year olds) tell them how cool it is to poop in the potty.
Sometimes we'll have them call one of the grandparents on speaker (everyone gets a kick out of that) to tell them how great pooping on the potty is.
Try not to be too dissappointed or upset with them if they are reluctant, just tell them how they get to wear really cool underwear and you are excited for them to poop and pee in the potty, because it is just so much fun.
Go to underwear as a rewards..get sme with really cool stuff on them - One of mine loved to see his name on them, so we used white underwear with his name written in sharpie and he loved it.
Also, it can be a good idea to go to the bathroom on a semi-regular basis, like every 60 or 90 or 120 minutes, and make it fun in there. They can read a sotry with you in there, or talk about something they like....
Bottom line, every kid is different - go with the flow (no pun intended). My kids are all uniquely motivated. Hopefully I've given some good ideas.