What kind of party will it be?  It can be a birthday party, a  wedding, a costume party, baby shower or any other kind.  This will help  you determine when and where to hold the party, what activities your  guests will participate in and also how the place will look.
Setting a budget for how much you can comfortably afford to spend is an important step in 
how to plan a party. Try not to go over your budget and if you are planning it for someone else, you must stay within their budget.
The next step is to plan when it will happen and then send out 
invitations.   Select a day when you know most of the guests will be able to attend.  It is best to plan this as early as possible. If you want to save 
money on invitations, you can email them.  Make sure you let the guests know what the occasion is.
Food should be planned in 
advance so the caterer or the 
person preparing the meals can purchase food and prepare it on time and in the  correct quantity to go around for everyone. Make sure you have serving  ware ready such as bowls, serving spoons, plates, knives, forks, spooks,  cups and glasses.
Plan the activities depending on the purpose of the function you are  holding.  You can have music and dancing regardless of the type of  party.  Games are also very popular but this will depend on the type of  party.  The type of music will also depend on the type of party you are  throwing.