First, day of FP is important. We usually arrive at the parks at 10ish. Our FP are usually for 10, 11 and 12. Somewhere in there we will eat lunch. Then, we have the rest of the day open for additional FP. While in line for our noon FP, we are scheduling another one so that we can hop right from that to the next. We usually have an entire TP schedule for the entire day planned out so we know where we will be all day and which rides have the shortest lines. But we usually end up getting a FP for that next ride anyway. Because even if the standby line is short, say 15 minutes for Small World, the FP line is probably walk straigth onto a boat so it still shaves 15 minutes off your days wait total. That way, you're constantly booking FP and almost never waiting. If your initial FPs are for the hardest to get rides, then for the rest there usually isn't a problem getting day of availability.
Also, we always spend more than one day in each park (except HS), so we dont always have to FP everything in the same day. So in Epcot, we will do FEA one day and Soarin another day because they both have limited day of availability. That way we dont have to compromise and do standby for the tier 1s that we we arent able to FP. We also like using evening EMH because that gives us additional time where the park is less crowded to ride anything we didnt get our day of FP and the standby was longer than we wanted to wait.
