I have had a few private messages asking me about "how do I become a tester"...so here is my response:

All I know is just put yourself out there, it someone says that they have created there own project, as if you could be a tester for them. I am also a member of crochetville and there is a forum there for designers looking for testers. The most important thing to do is ask a designer. If you have a favourite designer, and they are part of your group/forum/club, just ask them if you can test one of there patterns.
As most designers are looking for people to test out their writing of the pattern and how easy it is to follow, also if there is a problem with the design.
The most important thing is not to limit yourself with the experience level of a project. If you are not sure you can handle it but still want to have a go, let the person know that your not sure of your skill level but really want to test the pattern for them. Some designers arent looking for the experienced crocheter, but someone who is able to let them know if their directions are easy enough to follow and if there where anything confusing in the instructions. The designer is also there to help you, as you are helping them in the long run.

So the important things to remember are:
1) Ask the designer you want to test their pattern.
2) Dont limit yourself with the skill levels of patterns.
3) Give feedback to the designer on your progress.

In some cases the designer might ask you to test future patterns for them. But like always, ask to be a tester.