Problem selection:
For this drill, use climbs that are moderate for you – usually around your onsight level or below. You should eventually feel building fatigue, but not get so pumped that you start failing. The climbing time and rest time are not prescribed (thus, self-guided) but the goal is to accumulate higher capacity of climbing without resting so little that you power out. You could do some harder climbing, as long as you rest plenty.
Having a general goal for the session is helpful, like completing all of X grade or X circuit color in your gym. Harder grades/colors will obviously have higher intensity, which means a lower volume is possible. If the grade is too easy, we don’t get enough of a stimulus to actually challenge us.
So we want a high capacity of climbing, with some intensity. Try to find the grade/color where you can complete all the climbs in a session, but it is somewhat challenging.
If your gym is very small, you may want to pick two adjacent grades/colors and aim to complete both.
As usual, if you power out completely, the session is over. But because the climbing should be easier, power loss should take a while.
Climbing:
Climb at your own pace. This is a good session to do socially.
Focus:
Climb economically and smoothly. Other technical details may be suggested in your plan.