I am unable to answer you from experience, as I have not yet attained Team Leader status. I can answer you based on what I expect from my Team Leaders
I cannot name the single most important thing you must be doing, but I can name two - communicate, & never quit. Don't give up on yourself, & don' give up on your inactive sponsored affiliates - one day they may surprise you by choosing to become very active. Quitters never win & winners never quit.