I have gone through 11+ and independent school prep with my DS and DD. I feel I have learned a lot about the process and so have many others. Why not share this. The commonest pitfall is to leave preparation too late which just increases the stress. Hence staring this thread in the primary school section. My first suggestion is to look at as many as possible local secondary schools no later than the beginning of year 5, a year earlier would be better because you might want to consider to move house.
Sorry, I have to go but will continue later. Hope many of you will contribute.