We sat the test a couple of years back....
Looking around schools with DC is helpful - they get a feel for where they like / feel comfortable as well as having skin in the game to want to work towards...
I think you want your child to be 'capable' otherwise they may struggle when they get to grammar school. The 11+ is a lot around exam technique - knowing 3 areas, to move on, fill in the answer sheet correctly etc
Given above you don't have to 'tutor' too much but preparation in exam technique is worth it
Think about what works best for you & your family - a group tutoring situation may brings friends in a similar situation, some friendly rivalry, someone else doing the 'teaching' has an objective perspective, may have alternative techniques / explanations (in today's language that they use at school) and allows you to be parent. Can you work with your child?
Be aware of starting 'formal' prep too early - but encouraging reading, secure times tables are good, games & puzzles
Don't let it dominate your lives - there is life outside the 11+ - keep doing sports & other activities - if you need to do so much work then maybe grammar isn't right for you / your child
Build confidence in the 'how' to do a question before adding in timing / speed pressure
A mock exam is useful for as close to the real experience as possible (lets children be familiar with what is coming up) as well as the feedback on what areas you need to work on
Don't spend all summer holidays prepping - down time & relaxation is important
Have a plan for how you will handle failure as well as success - with friends, with your choices of schools
Reward the work & effort, not the result
Keep it all in perspective - easier said than done!
Only suggestions - you know your child best

Best of luck!