If you can order/buy a copy of Zita West's book that Sandra suggested, it's got lots of advice re. preparation for pregnancy and specifically pre- ivf treatment with a lot to say about diet, health, exercise etc.
Most of the pps have covered it - eat healthily, just the common sense stuff that everyone knows, more fibre, less saturated fat, get your 5 daily helpings of fresh fruit/veg, reduce alcohol to as low as you can, cut caffeine out - there are some very interesting stats on how it inhibits regular conception, drink plenty (but don't over do it either) water. I won' mention smoking as I assume anyone hoping to be pg soon will have given up already??? Are you taking a daily multi-vit yet? watch that it's a pre/pregnancy one as the regular kind have too much Vitamin A for those of us hoping to conceive. I'm also taking a fish oil supplement to get my DHA + EPA that Zita West recommends. There is a line of thought that says protein is important prior to conception too.
Lastly, dependant on your circumstances (ie. if you're using a sperm donor, don't bother with this next bit), DH should be preparing too. If your next treatment is June you've got the perfect chance for both of you to get ready. Zita has lots to say about male preparation too (I'm a bit of a convert as you can tell

). He can take a multi-vit too, reduce caffeine and alcohol. Plus, as sperm take 3mths to mature, it's a good idea to increase (at least) his sexual activity from 3mths before right up to treatment. This means his part of the deal is the best, freshest, most voluminous it can be. The rest is up to you!!
Good luck,
Debra.