Explain the purpose of going to the doctor. Tell it in simple, age-appropriate. For example, for the three years, just say, "There, the doctor will examine your body to see if you are healthy or not."
Try not to let your child be the first patient that day. Besides he did not have to wait too long, also in case when the doctor came too late. If the doctor until too late, might be disturbed child's bedtime and your step that would be overwhelmed.
Do not let the kids are hungry or bored, because he could be cranky during the visit. Provide your child with some snacks (preferably fingerfood) and favorite toy (a toy that is not too big and put in the bag). So fussy, take out one by one, yes, Ma.
If necessary, the child's lap. Many studies that prove children who lap their parents (rather than sleeping on the examining table) when injected or checked, not fear. This may be because they feel more secure and comfortable.
Arm yourself with a list of questions. Need not be too wordy, and stay focused on the child's health condition at the time! Also, lots of reading and browsing before asking anything.