The problem with this whole idea of "being ready to move up" is, that we are always shooting at a moving target. We never quite know, what our real luck adjusted winrate at the current stake is, we dont know, how much tougher (if at all) the next stake is, games change over time, and we also change over time.
So for me the best solution is to simply use some form of bankroll management and let that decide. Like for instance taking your total bankroll and deviding by 30 or 50 or whatever number, you decide, and then thats the highest stakes you can play. You can play lower, if you like, but never higher.
So using 30 as an example, if you have 657$ and play on a site, which offer 10NL and 20NL, then you are good to go to the 20NL tables, but you can also still continue to play 10NL or mix it up. If you drop below 600$ though, now its back to 10NL and rebuild. The bankroll dont need to be sitting in the cashier of a particular
poker site, but it is easier to manage that way especially in the beginning.
Of course this does not apply, if you have a million dollar and decide, that this is now your poker bankroll, even though you have never played high stakes before. I am talking about depositing an amount of money, which is enough for the micros, and then go from there. Like 100-500$, so that you start in fairly soft games and force yourself to build up from there.