The advice I would offer an aspiring young umpire is to be patient.
Do the apprenticeship and umpire as many matches as you can. Find a good coach and mentor. Make as many mistakes as you can at the lowest levels and learn quickly (from others). Never worry about matches you should be umpiring, just umpire that match in front of you the best you can and let the selectors take care of everything else. Focus on your game and what you can do – above all, enjoy it or find something else to be passionate about.