We used to use a paper diary system which was kept by the people running the hangar.....however now moved onto a Web based booking system, you can book months ahead or tomorrow.
I just got sick of paying £100 per hour for some shed of a PA28 that had one operational VOR, an interior that looked like a murder scene and an engine that would only start after some gentle coaxing from one of their engineers. The other problem was you could only book 2 slots on weekends - so you can't really go anywhere.
As your flying progresses you will also want an aircraft with a good nav fit, so you can do your IMC rating in it and some decent trips without worrying about Nav and getting the aircraft back in time.
I've also got shares in a twin (C401) for hour building.....just did an excellent trip to Toulouse (skiing) via Jersey, logged 12 multi engine hours P1 which I worked out cost me £90 per hour (you'll pay £350 an hour for that class of aircraft on hire).
If you want some advice on what to look for on a group aircraft PM me...
Cheers
Mer
Oh, forgot about the useage......it's gentlemans agreement really, as long as you don't hog it too much there's not a problem. We have a rule for each day you take it you must fly two hours min, and the max continuous you can book for is seven days.....so off to Spain in couple of weeks
Mer