I agree with everything Dan said.
It's hard to write a step-by-step guide since everyone's set up is different (hardware, online registration provider, pre-assigned vs dynamic bib assignment, paper vs paperless registration, and they could be running different versions of ART), the different types of races that people time, and many other factors that make a universal guide difficult. However I'll post some suggestions that I hope will help.
- The most important thing is to have a gameplan on how registration, check-in, and timing will flow and to simulate and practice that gameplan plenty of times prior to race day.
- Besides practicing the basics of just starting the race and accepting chip reads, practice how to handle manual adjustments (missed reads, changing participant info, adjusting the race clock, and anything else you think can happen on race day).
- Prior to race day, make sure you know exactly where the starting line, finish line, registration area, and which direction runners will be coming into the finish line.
- Also make sure your award break down in the software matches the awards they plan to hand out on race day.
- Show up early enough to get most (if not all) of your finish line set up and ready PRIOR to race day registration starting up.
- If you think it'll take 45 minutes to set up the finish line, I'd recommend showing up at least 90 minutes early the first couple of races until you get into a rhythm.
- Have your bibs/tags/registration stuff ready to hand off as soon as the race director arrives.
- Train them how to run registration and passing out bibs/tags so that you can be freed up to focus on the finish line or just floating around ensuring everything is going well.
- Have some kind of a backup system in place in case your laptop or any other core component of the main timing system fails.
- Another laptop doing manual timing, writing bib #s down in order if it's a smaller race, video camera, or any other method you feel comfortable with.