Before you do anything, you'll need a guest list. Save this one: party guest list to your computer, fill it in as you go or print it out and fill it in by hand.
Decide who and how many guests you will invite. Keep the guest list small the first few years of baby's life.
A good guide is to invite only twice as many children as the age of your child. A baby will be overwhelmed by the festivities as it is and too many other kids shrieking about will only add to baby's stress level. Family and friends will comprise the majority of your guests at baby's first few parties or until baby starts preschool or kindergarten.
Once your child starts school, there will be a pool of kids to choose from. You can be brave and invite the whole class or just a select few. If you know a particular child is a trouble maker, don't invite said tormentor. An out-of-control kid will ruin the party and your child will be miserable. In this case, invite only a select few and no one will feel singled out or individually excluded.
Plan on some of the parents staying until your child is about six. This will either be a blessing or a curse, depending on how you feel about said parents. Good advice: if a parent decides to stay (reasons being many: their child could be too young to leave unattended, scared to be left without a parent or they just want to ...) put that parent to work. You aren't there to entertain a bunch of kids and their parents or you would have specified such. Give them something to do, something that helps you and let the party evolve.
Until your child is about eight or nine, you will most likely be having co-ed parties. Enjoy these ... they will probably stop abruptly at around age 10 and won't resume until your child once again regains some semblance of hormonal normalcy at which time you'll have a whole new set of co-ed party issues to deal with. Do try to keep your child open to the suggestion of the opposite sex bestowing their presence on said parties. It will be a stab in the right emotional-stability direction but don't push it if your child has strong negative feelings toward inviting members of the opposing sex.