Phill Cappelle's Play Your Best 8 Ball is an excellent reference book.
Here's some 8 Ball videos that Max Ebere has done. These are really good because he goes through the thought process of choosing a group and picking patterns:
http://www.youtube.com/watch?v=FvWXmkg-QkM
http://www.youtube.com/watch?v=hrunGp5p5i0
http://www.youtube.com/watch?v=TEaDplqKicY
http://www.youtube.com/watch?v=GZhuthlkw7Q
When I first started playing league I would almost always try to get out. I'd often fall short a ball or two and at times this has cost me to lose, even against lesser opponents. A good opponent has a relatively easy out because you have now cleared all the traffic for him. And a savvy lesser player will make a a ball or two and then hook you, make a couple and hook you again - then get out. :angry:
My game improved when I realized that in every game there is a point of no return. Once you reach that point, if you go for the run out and don't get out you are in deep trouble. This may be different depending on each lay-out, earlier if there are problems like clusters. Keeping that I mind I've tried to consciously identify when this occurs in every rack. At that point I assess my chances to get out versus playing defense and ducking for cover. This is much better when you still have soldiers on the battlefield for defense than for a run out to stop a ball or two short, in which case all you've accomplished is having done all the heavy lifting for your opponent.
Especially when practicing I've found it useful on every shot to choose both an offensive shot AND the best defensive shot. This will open your mind to seeing those opportunities when a safety, even early in the game, is the better play. When you have problems in the layout a good early safety that gives you ball in hand will help you deal with those problems (like breaking up a cluster or a tied up 8 ball).
Deal with problems early if possible so if the break-out doesn't open things up like you hoped you still have balls to hide behind or create congestion for your opponent.
Best of luck and welcome to the forum! :wink: