Now that I can finally look at a score and mentally hear it, to a fairly high degree, I realize how important it is to mentally group things together. If you focus on a particular type of reading, you will see that there are not that many rhythmic patterns in a given measure. For example, if I see descending notes, I look to see if any of those are outside the key; then I look to see if they descend straight down, or go up by a step everything now and then. Rhythmically, are they all even 8ths, or 16ths? Are there 8ths with pairs of 16ths? Do the 16ths start on the first, second, third, or 4th beat of a 4/4 bar?
This may sound like way too much work for the task. But with practice, you can read patterns of pitch and rhythm instead of note-to-note, which is no good at all. This will help you pre-hear the music you are about to play, which you then play by hear, not by symbols.