Take your child to the store and let him choose his own toothbrush and toothpaste.
Try too not take control of this time, your toddler will want to be in charge, so maybe allow him to brush your teeth and you brush his making it more fun, or have a competition and offer a star chart reward, this could be on the back of the bathroom door.
These early lessons are as much about instilling the habit as they are about technique. The more practice he gets, the faster he’ll improve.