I flew with Ryanair earlier this year, I was fearing the worst but it was actually no different to flying with monarch on the same route the year before, except it was a third of the price and strangely there was more legroom than on the Monarch flight.
Everyone has covered the main points. I picked up one of these for my luggage
http://www.amazon.co.uk/Cabin-Max-Ba...8206529&sr=8-1
I also used the tips in the following articles, for better use of the limited space.
https://www.nytimes.com/slideshow/20...6-pack-ss.html
https://www.nytimes.com/2010/05/06/business/06PACK.html
Enjoy your trip