Collect copies of all your on-camera work. This generally includes copies of any television episodes you've been in as well as feature, independent, student and short films. You should also obtain copies of any television commercials you've done.
Separate your commercial clips from your theatrical work. You'll want to create a separate reel for your commercial and theatrical work.
Watch every scene in which you appear and choose the scenes that showcase you best.
Consider several things when choosing your best scenes to put on your reel. You want to make sure you are prominently featured in the scene and the filming is of good quality. No one will notice your talent if they are distracted by poor lighting and sound. Try to pick contrasting scenes for your demo reel. If you have a comedic scene, pair it with a more dramatic scene to show your range.
Choose the order that your scenes will appear. Feature your most notable work first. If one of your scenes is with a famous actor or on a well-known television show, consider placing this at the beginning of your reel to catch the viewer's attention. Oftentimes, casting directors do not watch entire reels so don't save your best work for the end of your reel.
Keep it short. Like most things in life, brevity is key in acting demo reels. Aim to keep your reel under three minutes. One-minute reels are very popular as casting executives are more likely to watch them, knowing it won't be a big time investment.
Get opinions from other people on the scenes you chose. Sometimes it helps to have a second set of eyes examine things as it can be hard to be objective of your own work. Ask friends and family if these scenes showcase you well and if they are good reel material.
Hire a professional editor to put your reel together, or if you have film editing software knowledge, you can compile it yourself. Your name and contact information should be featured at the beginning and end of your demo reel.