Use screenwriting software to format the script. Software like Final Draft and Movie Magic Screenwriter has the functions to properly format a screenplay and make work flow easier. Use the "Standard Screenplay Format."
Create a brief slug line to introduce the scene. Use "INT." for interior locations and "EXT." for exterior locations. For example, "INT. GARY'S GROCERY STORE - DAY." Use only "Day" or "Night," and save specific descriptions for the action lines.
Introduce any new locations in the first paragraph of action. Make it as visual as possible for animators. For example, "Few SHOPPERS fill the aisles at Gary's Grocery Store. Old cans sit on the shelf, flies buzz around and a lobster skeleton sits in the tank." Do this only for the introduction to each location unless the location has drastically changed.
Introduce characters in all capital letters. For example, "GARY, a weathered long-neck ostrich appears. He wears a red Gary's Grocery vest."
Limit scenes to two or three characters. This makes the animation easier to create and keeps the budget down.
Write out descriptive character actions. For example, instead of "Gary peers around the aisle to see PENNY PEACOCK," write "Gary stretches his long neck around the corner. PENNY PEACOCK's feathers glimmer in the air as she reaches for a box of cereal. Hearts replace the pupils in Gary's eyes."
Keep dialogue quick and to the point. Show character traits through the dialogue. For example, Gary could say, "Hello, Penny. Looking to save pennies at Gary's?" This shows his goofy side and nervousness with the attractive peacock.
Change to different scenes quickly. Even if the setting is a grocery store, you can jump from aisle to aisle or focus on different employees throughout the store.