Depending on which workout you're doing… When Going all out for 10-to-60 seconds try to maintain the same high speed thru-out.
Strive to go faster each 10-to-60 second burst (even if only by a little bit) but never go below 80% of your fastest speed. (For example… if you went 20mph on your first 30sec then try to maintain a speed of at least 16mph the entire workout)
Keep a workout log and try to burn more calories, go more miles and/or faster each time you do
any of these workouts.