First you have to define what it is. Are you truly talking about a carnival with booths for games, maybe rides, cakewalks, activities, etc.? Will you have an activity like Bingo? Concessions? Silent Auction?
To get started, assemble a bunch of people together and brainstorm. Lots of people have been involved in this or something similiar in other groups, church, etc. So everyone can contribute ideas.
Lay it out in a general plan and discuss how many volunteers you will need per activity, supplies, and how much advance work. (For instance, for a good silent auction, you should start months in advance.) Your brainstorming should produce more ideas than you can implement. This just involves rough estimates to help you get to the first cut. Details come later.
Make a first cut of ones you really want to do (carnival game??), don't want to do (pony rides??), or ones worth exploring (Bingo?).
Then tell us what those activities are and members of the forum can probably help.
A Spring Carnival is being talked about at our school. We have never done one before. Could someone possibly tell me the step by step process in beginning this endeavor. What needs to be done first? School day or weekend? Permit? Like I said, be specific.