I did mine recently - here are my tips:
1. Although officially reservations open up at 11am for your date, in practice they seem to open up earlier, some of the time at least. When I did it, the date opened up sometime between 8am and 8.15am (UK time). There are other posts on the board indicating that they have opened up at all sorts of times before 11am (6am Eastern), so it seems to be a bit random. Best to check regularly before 11am.
2. For me, the system struggled with some of the reservations, with the system crashing sometime between putting the ADRs in the basket and checking out. In these cases you lose the reservation and have to start again - by which time, the time you want may not be available. I would suggest doing only one or two at a time. It doesn't take long to check out. Also, one of the 'failures' was the California Grill which required a credit card guarantee - I don't know if that had anything to do with it (the credit card was fine!) so maybe that's one to do on its own.
3. If you have to call to book anything (such as the Candlelight package etc.) then you can call the number for the tours as well as the number for dining. When I was booking a tour, the (excellent) cast member told me that they are also able to do dining, and suggested calling them instead. In my experience, they were better cast members and I got through almost immediately in each case.