It's better if you DON'T write your introduction right away. Write it AFTER you've written your first draft of the body of your paper. Use your thesis statement and outline/plan (did you write one yet?) as your "roadmap" for getting the body of your paper well organized and staying on topic.
AFTER you've written your first draft, read your thesis statement and the draft aloud -- to yourself or someone else (or have someone read it to you) -- and get the body of the paper right FIRST.
Then you can worry about the introduction and, finally, the conclusion.
The entire writing process
Thesis statement, intro, and concl information here