Trust how you feel, and always adjust around the desired effort level.
If you feel good, go for it, rip it, go above and beyond.
If you feel “bad” (whatever that might mean today) ease up.
Recognize that good or bad are both temporary, so reevaluate your initial assessment after a few minutes and don’t let it determine how the entire session, day, or week will go.
Finally, always ease into any amount of effort with a little warm up.