Give a brief, attention-grabbing introduction to the subject. These are generally referred to as "hooks" and serve as a reason for the reader to continue reading. A good introduction not only grabs and keeps attention, but also grounds the reader and allows him or her to settle into the topic.
Touch briefly on your personal connection to the subject matter. This will increase your credibility. If readers see a first-hand connection between you and the subject, personal or professional, they will be compelled to read your forward, rather than just skip to the first chapter.
Avoid bragging or making the forward about you. While it is good to touch on your personal connection to the work, do not make the forward about you, your work or your accomplishments. The readers did not buy a book about you and will appreciate your forward more if it engages them in the subject.
Write about the cultural significance and relevance of the topic. Why is this biography timely and relevant? Discuss historical and cultural events that influence the subject of the book. For example, talk about how the current political climate relates to your subject if he is a political figure, or discuss how recent advances in technology make an old scientist's work important again.
Add important information about the edition, including how this edition is different from previous printings. Is it the anniversary edition of the first printing? Has new information surfaced that requires updating? Were previous editions enormously popular and this is a celebratory edition? Publishers look for this information, as it helps sell why the book is important.