1. Keep it short and sweet: Quality is definately above quantity here. Keep your reel under 2 minutes(under 1 if you don't have many clips). A client wants to see the range of your acting skills.
2. The newer the better: The older your clips are, the more you say: hey, I used to work, but I haven't practiced in a while. Keep your reel fresh!
3. Look for a variety of clips: If you want to highlight your physical acting skillls, don't make a entire reel that just shows your face! At the same time, you want a few closeups.
4. Have a nice intro: Do something to separate yourlself from the competition. What makes your reel stand out over others? Shock and awe!
5. A first impression: Put your best clip first, then work your way down. LIke a resume, the first few seconds tell the client what he wants to know about you.