The single most important thing is to be a profitable player. If you're not profitable, good bankroll management is only going to make sure that you go bust slowly rather than quickly. And as the easiest stakes to win at are the lowest, you have to ensure that you can make profits over an extended period at the lowest levels- NL2, $1 buy in tournaments.
So before you go anywhere else, or move up stakes, play at least 10k NL2
hands, and a lot more if you're not crushing it (>10bb/ 100, which is completely doable); or a large number of tournaments (not really my thing, but I understand that you need something like 1k tourneys for results to become reasonably accurate). Note that
freerolls don't count towards the 1k- this is a thousand $1 buy in STTs/ MTTs.
Only once you're sure you can beat the lowest stakes, and heavily, move up. If you're winning at 2bb/100 at NL2 and move up to NL5, you're likely to be ground down, even if you have the usual 30+ buy-ins. The standard goes up at every level. A losing NL2 player "taking a shot" at NL5 or, even worse, NL10 will be obliterated.
The number of posts on this forum from players who haven't done this is astonishing- players with a $20 bankroll who get frustrated by being called down at NL2 and think they'll win if players "respect their raises" blow it in a single session of NL5. SMH.