get into ones stride(to begin to do something in a confident and effective way after starting slowly: Both teams seem to have gotten into their stride in the second half.КГА)
fill one's boots(informal: Have as much of something as one wants; do something to the full: ‘fill your boots with spicy Szechuan food for under five bucks a plate' Bullfinch)
work one's way up to it(slowly build courage to do something; slowly work towards a particular position. Most people have to work their way up to jumping out of an airplane! Hvoya)
