You can't go wrong listening to the advice of Tattoo Dog!
Have you got your practice questions they send with the joining instructions yet? If you have, these are very similar but the most difficult of the ones they send you is equivalent to the easiest on the actual tests.
Look at the PQs, work out from them how long you have for each question on the actual tests. For most of them it's about 7 seconds. When you do the tests, stick with these times - if you can't answer, or are not working a question out after 5 seconds then move on. Speed is of the essence in the tests. If you can do quick arithmetic you should be ok. The verbal stuff - read a dictionary - there'll be words you've never heard of unless you've read one!
Remember as much as possible from the PLT demonstrations - once you've had these, the pictures in your cabin will make a bit more sense!
For the bleep test, look up what you should be expected to achieve as a member of the RN here:
RNFT standards and aim to at least reach this. It's not a big part of the overall score, but every point counts, so if you do some prep it's easy points. Male, 20 got to level 6-2, female, 18/19ish, got to level 4-5, both failed. Don't stop until you either die or you get your 3 misses
In the PLTs you need to be loud - make sure the board (watching from a distance) can hear you. In the leaderless task, try to naturally take charge of the others but be careful not to be overbearing - this is a team player assessment! In your task, be loud, lots of motivational stuff for your team and get stuck in with them. The comment about not getting the task done not making a difference, I'd be tempted to disagree - but that maybe the case for civilans. On my AIB 2 of 3 passed, the failure was the only one not to complete his task, on my oppos AIB, same thing. Perhaps they expect in service candidates to complete the task.
For the discussion exercise, remember as much as you can from the information you read, every little detail, from names to the time of sun rise and sunset, don't just concentrate on the scenario - they'll question you on everything. When you go into the board room for the discussion, make sure you get your input to the scenario but let others talk - it's a fine line between being left out of the group and being overbearing. You must hammer down about getting your aims, then prioritise the aims, then devise your plan to achieve the aims.
The quick fire questions - it's a nightmare! don't bluff, don't lose it and give it stacks of erm erm umm. If you don't know then say "I don't know" if you think you know, have a go and do it confidently. Find out a method of quickly calculating times to cover distances at whatever speed.
The interview, just tell them all about you. It's based around the information you put on your Q101 form. Examples of when you've been a leader, a team member, goals you've set yourself. Don't be afraid to mention when you've had something go wrong, as long as you can follow it up with how you fixed it! Know where the RN and UK armed forces are operating, maybe a bit about NATO and UN operations also.
From the time you get there, get to know the other 3 members of your board, the staff will harp on about this, but it helps if you get on with them and can work well with them
Hope this helps!