In reply to Spidermunkie:
Hi Col,
What no-one has mentioned yet is the one thing I see a lot at the crag and that's the belayer standing in the wrong place. I consider the basics to be:
postiton - if the leader falls off before getting gear in, where will they land? You don't want them to land on you. On single pitch routes, especially with a poor landing your role is that of spotter. Once the first runner goes in, consider is it a nut, sling or cam? What will the direction of load be on it? It's crucial to learn that when the leader comes off, the rope will make the straightest line possible between runner and your belay device. If the first of a number of runners is a nut and you are not stood with your foot (at the very least) against the rock, then that nut *will* twist, probably invert and possibly come out.
Pay attention - it's your job to watch your leader and anticipate their needs. When will they need rope? Which rope will they want to clip next, what if they drop a piece of gear? Will it hit you? What happens if they fall off?
My pet hates - belayer not watching you but admiring the view. Take up hillwalking if you don't want any responsibility. It is possible to do both well.
Belayer lying down 10ft from the crag. Take up sunbathing. You are a hazard.
These, to me, are the fundamentals along with understanding your leader's wishes. Do they want encouragement? Silence? Are they likely to want you to photograph their arse at some point? If so, can you lock them off safely and do it one handed, prepared to drop your camera if necessary?
Once these are mastered, on harder routes you may have to get creative. That's where things like 3 rope belay systems, back ropes, pulleys, taking in slack, jumping off ledges etc may be employed. I've never had to do much more than pay attention stand close in and lock off though.
Phil