First off, always keep your guitar in an average temperature. Never carry your guitar outside with no cover (unless performing). Wipe the dust of your guitar frequently to reduce the possiblity of a breakage. These are just some of the things that you probably already know about. I just wanted to cover them.
Ok, here are some of the things that I do. I am one of those guitarists who wants to make the strings last as long as possible so I dont change them on a regular basis. I always change them when they break, or when they are a pain in the ass to tune or when they are all messed up with fret indents and rust. Most of you probably change on a regular basis so I dont want to read any lame comments about how there is a difference there.
One thing I do is try to always keep my guitar inside of its gig bag when I am not using it or playing it. This will keep the strings from getting covered with dust and it will reduce the time it takes for them to erode in oxegen.
It also helps to always after taking a string off to look carefully at the bridge, neck, and tuning machines. If you look closely, you could possibly find a small ident or a crink in the metal. These can be the number one reason for strings constantly breaking. If you see one of these, contact your local guitar repair shop (most music stores can fix them). What they will do is fill the indent up with pencil graphite and/or file the crinks down. (by the way, I'm not sure how you spell "crink" so dont be too harsh).
After putting the string(s) on my guitar, I always tune them very slowly. What I usually do is put the string on and tighten it halfway. Then in about an hour, I tune it very slowly the rest of the way up. The reason for this is that when a string is taken out of its package it is immediatly introduced to a different temperature and a different air chemical. If it is tightened all the way really quickly, the odds are it will break right then, if not within a few days. If you give the string(s) time to stretch, adjust to the air and temperature, and become fitted into the guitar, they will play much better and wont break as easily.
Another thing is when you have extra string at the tuning machine of your guitar, always wait a day or two before clipping it off. Usually they dont but sometimes strings can slide out of the knob after being put on. If you have a trimmed string, it could slip completely off and you wouldnt be able to reuse it. When you have extra string, it can slide down without falling off and you wont have to (re)restring. Believe me, if it happens to you it will "piss ya off".
Well this isnt really an official guite to strings but I find these things very effective when restringing my guitar. I hope these tips can work for someone else too.