I just got back from the first preview and I have to say I was much more impressed than what I had expected. The crowds were few during our preview but even so, we didn't get to see everything because there was so much to explore!
First tip: You WILL get wet on the Grizzly River Raft Ride. If you go on it, make sure it is warm outside, or that you have a rain poncho so you don't get soaked. Also, if you get dizzy easily, note that the rafts spin a lot.
Second tip: The longest line will most likely be for Soarin', which is a great attraction. If the Fast Pass is working, make sure you get one.
Third tip: Keep your head on the headrest on the California Screamin' roller coaster. The launch is sudden and I sure didn't expect it. It's a lot of fun and surprisingly smooth.
Fourth tip: When the parade starts, make sure you're standing someplace where you can move around. If you find that you need to leave or go someplace else during the parade, note that there weren't any crossing areas and we had to wait for the parade to complete before we could cross.
Just some notes from our trip, we really enjoyed the Maliboomer. It's not as frightening as it looks and it is really smooth. The Avalon Cove restaurant is pricey but it's good. The Midway games at Paradise Pier have nice prizes. They don't seem to be the cheap toys you see at carnivals. Take time to explore the Animation attraction. It's like an exhibit hall with several things to see. We didn't get to it but I hear that the Steps In Time show at the Hyperion Theatre is very good.
Overall, our whole family really enjoyed the park and are waiting to go back. Have a great time at your preview! You'll enjoy yourself. Take money because the merchandise is mostly DCA exclusive and very nice. They do have Package Express so that you don't have to carry your purchases around all day.