Writing a thesis is an arduous, trying job. After all that work the last thing you can afford to do is write a poor abstract. The thesis abstract is one of the most important parts of the thesis writing process. It can be a huge factor in influencing your reader's decision to read your thesis and the reader's judgment about its quality and importance.
Write your abstract last, after completing the final draft of your thesis. If you write it any earlier you run the risk of it not being as accurate as it should be.
Keep it brief. Be precise and concrete in the language you use. Your abstract should be no longer than two paragraphs in length.
State why your thesis is important and worth reading. You need to sell your reader on your work.
Give the reader an idea of what to expect by giving a context and overview of the argument or results.
Include important words and phrases that can be found in the larger work. This way a search engine is more likely to single out your thesis.