I realise this is a bit old now, but I'll write about my experience.
It took me only a week to get an appointment for fingerprints at the Wakefield police training place, and I just paid £20. I printed off the FBI fingerprint card sheet on regular paper (of course I made several copies in case of mistakes). I had my fingerprints rolled on and the guy who did it put a stamp on the back of the paper, signed it then signed the front. If you can find thicker paper, that would probably be better.
I then filled out the application form for the FBI check, and another application for the US state department to receive an apostille. I stuck a note and letter in to let the FBI know to authenticate my results since that's required for an apostille.
I got 2 prepaid usps priority mail envelopes, one addressed to the US state department (from the FBI), and the other addressed to my mom in the US (from the US state department, and so she can send it back to me).
I did this all while I was in the UK, and it took a while to put everything together. There may be a lot of ways to doing this, but this is the way I did it and it worked for me. I only got the apostille just to cover myself, since I am not sure how some employers or whatever may react without it.
Just to give an idea of the time frame for processing: I sent my package from the UK to the FBI on January 25, 2012, the FBI finished processing it in the beginning of March, the State department received the next package on March 3rd, and my mom received the package on March 23rd.
I personally started this whole process in the middle of November with the fingerprints, but it took me a while to figure out how to put it all together. Even though my application was rather sloppy, it was still successful. I suppose a suggestion would be not to worry about it too much, because I know I did - it's a very convoluted process.
Another thing is to check the FBI website for information on the background check application process and the US State Department website for the authentication application process. Their requirements change often, such as the State Department changed their's while my application was out of my hands. Thankfully that didn't cause any problems for me. http://www.fbi.gov/about-us/cjis/background-checks
- FBI Criminal Background Check http://www.state.gov/m/a/auth/
- US State Department Office of Authentications
I hope that was a little helpful at least.