I had a pm from someone about agents and it made me think. I've only picked up the information I have and feel able to pass on tips and advice because of some really rather painful experiences! I suppose that's how we all learn. I wish I had asked more questions though, and I wish I had bothered to find out what really happened in the industry rather than just making assumptions about what I thought and hoped happened in the industry.
Here's a run-down of sensible pg's lifetime experience of agencies - looking back I realise it's even worse than I recounted in my pm

Before I went to drama school:
A friend introduced me to an extras agency. I paid some money to be on their books and had a few jobs. I then started finding out a bit more about them and realised that the contract I had signed was OUTRAGEOUS. Honestly: 35% commission and if you had to cancel they would charge you the equivalent of what their commission would have been, even though you would not have earned anything. The company closed down because of all sorts of nefarious dealings, some of them really unpleasant. I think I had a lucky escape.
My next bad decision, many years ago, was to send off £15 to an "extras agency" who advertised in The Stage. I didn't do any research, I took what they said at face value, I didn't know anything about how the profession worked etc.etc. Amazingly, I never heard from them again! Well, how extraordinary is that?

I then did a bit of research and signed with a different extras agency. They had lots of experience and I had a few jobs through them. There were no real problems. Then I decided that I wanted to try to work as an actor, rather than an extra.
My next, not entirely brilliant decision was to sign with an agent who was also an actor. He was lovely actually - a really nice man who tried his best for his clients I think. He didn't have the greatest of contacts though and he couldn't really dedicate himself properly to his clients while he was trying to work as an actor. I eventually decided that I needed to try to find an agent with a bit more experience. My next BAD decision was to sign with an agent who had never seen me perform (though I did have an interview with them). I knew, in my heart of hearts, that the fact that they were willing to take me on without knowing whether I was any good was a really bad sign. I raised this at the interview, but I allowed them to flatter me by saying "they could just tell" and "I came across very well in an interview". I really wanted representation, they'd been in the business for a while and I didn't turn the offer down. I never got any work through them and when I asked to see a copy of the CV they were sending out I was horrified: badly typed, full of spelling errors - it even had someone else's training on it! I ditched them.
I then signed up to an "agent" which had an "on-line" presence when this was in its infancy. It didn't cost me anything. I didn't get any jobs either! It took me a while to get them to take my details OFF their website.
Next (because by now I was really very wise of course

I left that agent...
Then I went to drama school. I didn't get an agent straight from drama school, but I did manage to get an agent (my current one) within about 6 months of leaving. By then I was at least a little bit wiser and knew a lot more about the industry!!
I do think that communication is probably the most important thing in a client/agent relationship. I don't actually communicate all that much with my agent, but we did have a clear conversation at the start and I do know that she will answer any email questions very quickly and that if I need to, I can phone her up and have a conversation. She also knows that I won't bother her by phone unless email won't do and this arrangement seems to work very well. She's quite "cool" in her manner, though always pleasant. I do trust her - and I think that's the vital thing.
So, as I say, I'm much older and a little bit wiser but oh boy have I made some spectacularly bad decisions in the past! I wish I had had someone I could have asked. That's why I love this site!