Well I know my nash push fold quite well for up to 15 BB, and I generally stick to them unless the opponent is really crazy. It changes a bit with ICM, and obviously I have a different range if someone has raised, but it's all chart/ math based and so it's quite easy to learn. (Examples: http://www.pushfoldcharts.com/)
. As for how many BB I start to shove at, it really depends. If I am on the button against two nits, I might just raise with 12BB, because they are often inelastic and will call a shove if they call a raise, but if I am in early position, I might shove up to 20-25BB. It really just depends, as with a lot of things in poker.
Actually that's not true. If I decide to reg a micro stakes reg speed tourney early and I have 1000BB, I'm gonna shove with aces. People call with too much