Research is your first step in pre-production. Before you actually start working on your project you need to have some idea of what it is you'll actually be creating and how you'll go about doing it.
Tutorials
It's helpful to have a tutorial to fall back onto if you want to achieve a specific effect that you don't know how to do. Tutorials are also a good measure of how long that specific effect will take and if you can complete it in the time allotted. For example, if you plan on animating an airplane flying through 3d clouds and have never created 3d clouds before you'll want to look up tutorials demonstrating how to do it. If you don't have any idea of how to tackle an important aspect of your project like that and leave it to later stages, you may find that you didn't anticipate the increased time it takes to download additional software, set them up, animate, and then render it all.
Remember - Google is your friend.
Reference and Mood Boards
References are images or video you gathered for inspiration. Video references for animation can be filmed yourself, or found online or from other resources. It can also be as simple as asking a friend to do a motion and observe them doing it, or think about how your body moves when doing it yourself. A reference or mood board is generally a collection of images with specific details you'll try to replicate or a look and feel you may try to explore in your work.
You can also make mood and reference boards for environments or props.