These are the 3 principles I find to be most powerful for creating routines and are implemented in 8reps.io

Repetitions, not perfections
The single most important factor to create a routine is to simply do the habit you want to establish. It is much less important to be perfect at it all the time. Let’s say your goal is 30 minutes of cardio exercise every morning, but on some days you only have 5 minutes of time. On those days the workout is not perfect, but you still get the habit into your mental wiring.

Don’t miss twice
On some days, it is simply impossible to do every planned routine. However, try to never miss a second day in a row, as this might interrupt the formation and maintenance of a habit.

Plan and review planning
Consciously plan your daily routine and revise your planning if necessary. A daily protocol is never set in stone, but needs adjustments from time to time.