Finchlark, if you want to be a part of real-life critique group, instead of submitting stuff online, I'd suggest taking a class at a local community college or joning a local writing club. That's how I met the members of my critique group, we've been meeting once a month for almost 2 years and it's really helpful.
Joining SCBWI is a very good idea, too. Some regions are more active than others, but most have some sort of email list or website to help people connect with other writers looking to join a critique group. Attending conferences is great, too. At most conferences you can pay a small fee ($35-50) and an agent, editor or published author will give you a personal critique of up to 20 pages of your work. It can be very helpful, but since we're not ultimately judged by the first 20 pages, it's important to have other people who can take the time to read your whole book, as well.
I actually worked with a professional writing coach (yeah, I paid money.) Some people would argue that you don't need to pay for a critique group, and that's true. However, your critique partners can only teach you as much as they know, and I was hitting the wall of not-quite-good-enough but I didn't know why. It was definitely worth the money to work with someone who really understands how to make a plot compelling.
If you're interested, send me a private message and I'll give you his information.