Hessayon suggests that in the winter, February, take out dead and diseased wood, crossing branches, and vigorous laterals crowding the centre. Some apples are tip bearers, so go easy on the laterals. Look to see if there is a fruit bud on the tip, and leave them alone (tip bearer). Some apples are spur bearers, that is they set fruit closer to the lateral, on short spurs. A leader is a shoot going upwards. There may be several. It's up to you whether you leave all of them. If the tree has been overcropping a lot of small apples, and is spur bearing.....remove some of the spurs on the inside of the tree. The aim is to keep the middle more open and keep shape and framework on the outside. In February you can see what to do and the tree is dormant.