There were a few threads on this a year ago, scroll to about page 11 (or older) on the index
here is a link as an exampleviewtopic.php?f=30&t=35136
This will be the third year. Two years ago the girls went in blind, no advance info had been released on formats, types, lengths, number of questions etc. Last year everyone was more wise to probable format (but it was suggested marked hard as it is marked by staff more used to doing KS3, KS4, KS5 so unlikely to be charitable with half marks for basic mistakes).
A good practice comprehension is to get a random picture and get it described in an essay, eg set the scene, enhance it with a good descriptive paragraph (creative descriptive words), and remember to wrap up the story at the end. Remember some year 6 wont yet have been taught how to structure a essay (to avoid it reading like a disjointed list), but need to be able to do it to get good marks in the comprehension.
For maths and other English, just practice the questions in 11+ (for 11 or 12 year old levels), or KS2 revision questions aimed at level 5, this will be slightly harder than the real questions (or more strictly will cover a greater syllabus)