If you plan to see both parks than definitely start at Islands of Adventure, get there at opening. It gets more crowded. I can PM you with details on what to skip, to get on to the better rides
Bring throwaway rain ponchos for the "water" rides, you will get soaked on Bluto's , Dudley Do Right and possibly Jurassic Park ride. These are situated near each other. I buy the $.59-$.89 camping ponchos in Walmart, then chuck them in the garbage after finishing these rides. Or , if I am feeling generous, I give them to another family.
They don't have "fast-pass". They charge $25.00 per person for an all-day "fast-pass". Not worth it. These parks may not be so crowded in May.
Though I am new to this board I am a veteran at these parks. Please PM me if you need more detail. Have a great time.