When you play, try to identify the patterns your playing. think about the way the mapper has mapped the song. If you can't do this while you're playing without getting bad scores, you're not at the skill level where this will matter anyway.
It's natural to lose skill after a long break, and it can take time to build back up to where you were. Lower reading speed might help this process, but even if it does, it probably won't be a big effect.
So, As you improve at the game, being able to hit notes should become basically automatic for you. If you can think about all sorts of other things and still play the song properly, you're at the stage where you can begin paying attention to patterns more closely to the actual patterns themselves.
What I do when I play maps is try to identify exactly what sounds each note follows. I also analyze it like I would if I was mapping it. I look for any inconsistencies in patterns. I look for how the mapper transitions between different patterns. That sort of thing.
Vertical and Horizontal reading are just 2 different ways to look at a pattern. I use both at the same time on maps I'm not familiar with.