Have been for the last 4 years (finger crossed this year as well) and it is well worth it. As for tips it does depend on what your interests are as there are lots of interesting things to see and do. The show grounds have aircraft parking area such as warbird / vintage / homebuilts / ultralights so plenty to choose from there. It is also possible to take flights in a Ford Trimotor (book early for this) and a Bell 47 which operates from the Museum (again get there early) The museum itself is worth a visit especially if one of the days is poor weatherwise. It is also possible to fly in the EAA B17 but again it is best to book this a few weeks in advance. Make a plan for each day and try to stick to it - otherwise you will end up with a case of 'headless chicken' syndrome.
Wear comfortable walking shoes / sunscreen & a water bottle - there are plenty of taps to fill up at. If you are after any clothing then get them early as sometimes they do run out of popular items. Each day a paper is published giving details of the flying display during the afternoon - very handy for not missing something. (look out for the DC3 mass arrival on Monday) The paper also details the various speakers etc and they have some fascinating lectures
(last year they had the crew of the A320 that ditched in the Hudson + many more)
Look at the EAA website for map of the grounds and try to pick out some of the areas that might be of interest. The grounds also have a 'tram' network which is great for getting around + saving the feet.
Any more info then drop me a line and I will see if I can help