Film as many games as possible. In-game footage is important for use in a highlight, as hitting well in batting practice is not likely to impress a coach the way in-game highlights will.
Include footage of successful at bats, highlighting all strengths of your game. Showing home runs will impress a coach, but so will showing doubles and clutch hitting with runners in scoring positions.
Include footage of plays that highlight strong fielding, such as good catches or stops, instances of throwing runners out if you play outfield or catcher, and striking out batters as a pitcher.
Keep the length of the video brief. A long video can dissuade a coach, who is likely to be receiving many videos, while a shorter video tells him he can see what you are offering without investing too much time. Two to three minutes is ideal.
Upload the video to YouTube, allowing you to distribute it online instead of sending physical tapes or DVDs.
E-mail coaches at schools you wish to be scouted by with a link and one or two paragraphs expressing who you are, your interest in their programs and what you can bring to their teams.