For most, it's effective to divide training into 3 zones — typically these are determined off maximum heart rate (MHR), but can also be determined by perceived effort
If you don't know your maximum or peak heart rate, it can be estimated by subtracting your age from 220
75% of training should be at 60-80% MHR or moderate effort
20% of training should be at 80-90% MHR or moderate-hard effort
5% of training should be at 90%+ MHR or hard-very hard effort