Here's a wonderful, informative website you might find helpful. It gives a few variations on"readiness" checklists, plus tips on various training strategies, the best ages to start them, and the advantages and disadvantages of each approach: http://www.parentingscience.com/toilet-training-readiness...
The "happiest" experiences that I've observed (and practiced myself when my daughter was little) was to do lots of "pretraining" with demonstrations, books, role-play with toys, videos, etc. When the child is ready, usually no earlier than 2 years and a few months, he or she expresses the desire to use the potty and wear real underpants.
At that point, success usually follows quickly, sometimes in a couple of days or a week. I've seen instances where there was no more than one accident. When accidents do occur, calmly help the child clean up, and express your confidence in his ability to figure it out pretty soon.
Be aware of a few things: Some children won't be ready until age 3, 3.5, or 4. Night dryness comes in its own time, and can't be "taught." It depends on the body and brain maturing, and is not in the child's control. And poop training is actually a separate step for many children. Some master it first, some right along with pee training, but many kids need extra time to work on it, especially if they have any problems with constipation or uncomfortable pooping.
Good luck! Do your best to stay casual and supportive, and it should go well.