Now is a good time to cut back any long shoots. But you may lose some of this year's fruit buds. Cut back all secondary side shoots to about 3 leaf scars. And take out any congested or crossing branches, also any dead or diseased bits.

Depends on whether it is a tip bearer or a spur bearer. What variety is it? In general terms unless it's a 'minarette' type, you need to prune it to achieve a bush shape with several main branches, and avoiding them crossing or filling up the middle. Any pot grown fruit needs careful watering and FEEDING though during the growing season if you are to get any reasonable amount of fruit.
Determining the general way of pruning and identifying the type of pruning necessary is covered on this website:

http://www.ehow.com/how_5649457_tell-spur-bearing-apple-trees.html