Start with a good warm-up. The warm-up below is more descriptive than prescriptive. If it takes you a little longer to warm-up, ta all the time you need.
The main set is very prescriptive. The first 5-minutes is an all-out effort. Remember your Threshold Power is an aerobic activity. By making an all-out effort, it will minimize how much your anaerobic system will contribute to your FTP test. Easy pedal for 5-minutes. When you are ready for the 20-minute effort, hit the lap button and go at it. Do not start off as if it were a sprint, stay in the saddle and go hard. Settle into a rhythm and hold a power that you believe you can do for twenty minutes. At the end of the test, cool down.
Upload your workout to Training Peaks. If you did not have an FTP calculated in the software and notifications are set on, the software will determine your new FTP and email you a sweet little note. You can also go into the workout and select your peak 20-minutes. Take that average power number and multiply it by 95%. This will give you your FTP. Add this number to your TrainingPeaks setting and calculate Threshold Power, Andy Coggan (6) method and this will set your training zones.