Any Tips On Freelancing?

I currently work as copy writer for a PR firm in the industrial sector. To say that the job is a little dull would be a complete waste of the opportunity to use the phrase "a monotonous exercise in the exceedingly mundane".

I would like to explore more stimulating forms of writing in a professional sphere, earn a little extra cash and expand my horizons. Freelance immediately springs to mind. Unfortunately I have absolutely zero experience, when it comes to finding freelance work.

I would appreciate a little bit of input from anybody who has had any experience in this regard.

Basically what I need to know is:
-Where to look for work
-What a portfolio should include - I'm loathe to use the stuff that I write for work.
-What is the going rate for freelance work
-Any tips on travel writing would make my day
-The same goes for opinion pieces
-Any thing that you can recommend which have missed - pitfalls/benefits etc.

Thanks to anyone who takes the time to respond. Your input is much appreciated.