Your introduction will usually be a paragraph of 50 to 150 words (in a longer paper, it may be more than one paragraph). Perhaps the most common strategy is to open the paragraph with a few sentences that engage the reader and establish your purpose for writing. You can then conclude with your main point, or thesis.
Characteristics of effective thesis statements
Testing a working thesis
Effective thesis statements
Exercise: Introductions
Exercise: Thesis statements 1
Exercise: Thesis statements 2
Related topics:
Writing an introduction
Placing the thesis statement within the introduction
Drafting the body
Drafting a conclusion