Buying fun new underwear for them can act as further encouragement.

If your child seems to be afraid of the toilet itself, then gradually acclimatize him or her to the potty. Have them sit on one of the little potties fully clothed for a few minutes each day while you read or tell them a story

Begin putting the contents of their dirty diapers in the potty so they can see what happens. Then give them the opportunity to run around bare-bottomed so they can try to go on the potty if they want

Try reading aloud (together) one of the outstanding books that describe potty use as a part of growing up. My favorite is Toilet Learning by Alison Mack

At this age best is to reward him for good behaviour.A star chart works.Every time the child goes to the bathroom "on time" they get a sticker and for each 5 or so stickers they get a small toy.

Toilet Training for Boys:
10 Tips - of them one listed..
Another way to get him excited is to put one blue food coloring in the toilet. Tell your son to watch as his pee changes the colour to green!
http://tinyurl.com/4ym3yf

Convey the message of good behaviour through stories.During the initial days make yourself available near them, divert their attention, talk to them and ofcourse reward them at the end of each episode.

Teach the boy to aim accurately by having him "sink the battleship. Stick some cherrios in the toliet and have him aim at it!