For the entry level ASE's, best thing to do is to start working in the shop. Get some hands-on experience with different vehicles brakes and suspension systems (most popular ASE tests).

Not sure what your work status and stuff is. But even if you just start out as an oil change tech and cleaning the floors, and shadowing some of the more experienced techs... you'll move up the chain in no time by being respectful and ready to learn.

If you go and get your ASE's and then walk into a shop with practically no real hands on experience (working on our own vehicles doesn't really count, shop environments are completely different), you're not going to get very far. I've trained my fair share of techs... the ones who make it are the ones who aren't "too good to sweep the floors or stack tires". That's also how I started. Even though I grew up building cars/trucks/etc and was in my neighbors auto shop every weekend, when i was old enough to work i started out as an oil change tech. When I wasn't busy I would hang with the top techs and give them a hand, ask questions, etc. I would also help them solve issues they didn't understand (thats the engineer part of me).