Disclaimer: before taking on this training, consult your doctor and see if riding this hard is good for you. This is high intensity and hi tension work.
Step #1: Pick your measuring protocol
You have 3 options to measure your effort here. The best option is power. Power will give you a reliable, precise, accurate measure of your effort that will not change over time. The second option is perceived exertion. Perceived exertion is a measurement scale from 1 to 10 but it's completely subjective. It is how you feel and rate your feeling of effort. If a 1-minute max effort is a 10, then these should be around a 7. Remember you need to do 20 of them. And the third option is really the worst and that is heart rate. I'm not saying that heart rate isn't a good measure of effort but what I am saying is that for a 1-minute interval, your heart rate will lag too far behind for it to be an accurate measure.
Step #2: Pick your course
Ideally, the best course to do these types of intervals is a closed course with about 2 miles of open road. But we don't always have that available to us. 1 Minute Intervals offer a much greater degree of flexibility in terrain because the short intervals have such a lower likelihood of being interrupted by stoplights. You also need to think about what you're trying to accomplish with these intervals. If you're trying to build the power to break away on a flat 1-mile crit course, then do these on a flat 1-mile crit course. If you're doing these to be able to power over a hill on your local group ride, do them on a hill. If there is one thing I know about training is that whatever you do and repeat you will get better at. That's how your body adapts.
Step #3: Keep your cadence under 95
The goal of this workout is to build power through tension. If your cadence goes up over 95, you'll be taxing your aerobic system more than is intended. There is a time and place for one-minute intervals at high cadence but this isn't it. This workout mimics a criterium race because you don't always have the luxury or might not be able to pick the right gear to respond to a surge or attack.
Step 4: Lightly refuel during the ride
As this interval session taxes your glycogen stores massively, it is very important to bring two bottles with one bottle containing an endurance drink of sorts. One light sip of the endurance drink between intervals will reduce the pain a bit. Any large amount of food consumed could come back to haunt you after 15 intervals or so.
Step 5: Recover properly between intervals
I believe that light pedaling is more effective at recovery than going totally off. In my time between intervals, I spend about 3 minutes at 125-150 watts going nice and easy around 80 cadence.
To see how I've done mine in the past, have a look at the youtube video below. Be sure to pick the intensity that you know you can safely do repeatedly 20 times.