Happy to do it! This is the question I've gotten most. It's probably worth a future blog post, but I'll give you the short answer I've been giving others so far. The best thing is word of mouth. Once you have some happy clients, they will tell others. Mention to friends and other developers that you know that you're looking for contract work, and they will very often pass your name along to people. Sell your own apps, sometimes people will find them, contact you and ask you to do stuff that is similar. Finally, give boards like Elance a shot, but don't sell yourself short and take $15/hr jobs if you can't live on that.

As for your second question, I'm never 100% comfortable about this, which is kind of fun. I never know what someone is going to ask me to do next, but the API docs are good, the community is helpful and it's a fun platform to work on. There's lots of answers out there if you need them. However, I can tell you there are important things to know. For one, memory management is vital on iOS devices. The OS can and will remorselessly kill your app for using too much, without warning. Memory overuse is a crashing bug, do whatever you must to squash it dead.