If you are graduating from a Run Bike (Balance Bike) to a Pedal bike here is a good tip.
Your child will already have a good handle on balance. The thing they need to learn is pedalling so start them learning on a gradual slope. This way the bike will coast down slowly while they work on figuring out the pedalling. Balance is natural to them at this stage so if they only have to worry about pedalling it makes it an easier transition.
Give it a few tries over a few days and you should find your child gets the hang of it well. It's different for every kid though, so be patient. The temptation will be there to put training wheels on but stick with your child and they will pick it up much faster than going to training wheels.
This tip comes from the experience of graduating 2 four-year-olds to a pedal bike from a balance bike.
And always make it fun!