Most authors agree that it is harder to write a short description of something than a long one. Here's a tip: for your first draft, don't be overly concerned about the length. Just make sure you include all the key information. Then take your draft and start crossing out words, phrases, and sentences that are less important than others. Look for places where you can combine sentences in ways that shorten the total length. Put it aside for a while, then come back and re-read your draft. With a fresh eye, you'll probably find new places to cut. Before you know it you will have a tightly written abstract.
If you need to write an abstract for an academic or scientific paper, don't panic! Your abstract is simply a short, standalone summary of the work or paper that others can use as an overview.  An abstract describes what you do in your essay, whether it’s a scientific experiment or a literary analysis paper. It should help your reader understand the paper and help people searching for this paper decide whether it suits their purposes prior to reading. To write an abstract, finish your paper first, then type a summary that identifies the purpose, problem, methods, results, and conclusion of your work. After you get the details down, all that's left is to format it correctly. Since an abstract is only a summary of the work you've already done, it's easy to accomplish!