We've been DIYing for 11+ for the last year on and off - it's in just over a week so nearly out of the other side!
We started drilling times tables - which was also done at school anyway - by printing off worksheets, 100 questions in 4 minutes. If you Google there are a few websites that offer to create worksheets for you based on what tables you want to do and if you want mixed operations (division as well). Once those were comfortably answered in the time, we moved on to other topics.
We used the Khan Academy website to learn the stuff that hadn't been covered at school, got through that by Easter of year 5, then have been working on familiarisation with the format and speed since. We have also used Schofield & Sims Mental Arithmetic books.
Familiarisation has been done with mocks provided by our local grammars (which you have to book a place on in around January, the mocks are in May/June mostly), plus GL Assessments mock papers, and First Past the Post mock papers - the last allow you to do an online comparison of how your child performed against everyone else who has ever done that mock paper.
All of this though does depend on what style of 11+ your child will sit - our preparation has been for the Sutton superselectives, and this approach has fitted their format of purely English and Maths papers.
Other things we were recommend to use for English (and did use a bit, towards the beginning):
Rose McGowan - 11+ Vocabulary
Stephan Curran - English Spelling & Vocabulary books 6-12
Haydn Perry - Once a Week Comprehension books 3 & 4.
Hope that helps, good luck.