Which exchange is likely to offer the best rates? Should I register with a couple?
You can see a list of current exchange rates
here and
here.
How do I protect myself from the dangers of using an exchange? i.e. I know not to use a wallet provided by an exchange.
The standard security practices that anyone using a computer should know are sufficient. Also watch out for phishing email and whatnot.
It is best to register onto a known/good exchange depending on your region. For example, I'd suggest
Gemini if you're in the US and
Bitstamp if you're in the EU.