There actually has been a thread made about this topic, but unfortunately I cannot find it.
The general consensus from what I recall from that thread was...there was none. People had different preferences. But I'll tell you mine's.
I would look close to the arrow receptors just so that you can be sure you know when exactly to hit those arrows. It's very easy to look further down in anticipation of what comes next but I find that your mind makes a lot of erroneous assumptions in a game that requires more or less precise timing. Even if the song is perfectly synced and you think you know what's going to happen next, you really don't see what you're hitting - and that can result in what we might say are "random" goods that we didn't see.
So you can either resort to: a) increasing your speedmod so that what you see below is very quickly going to be what you're hitting, or b) lower your speedmod a bit and look at the arrow receptors to reassure what you're hitting at the right

*to reassure what you're hitting at the right time. I chose this second option a while ago and it improved my accuracy. But now that I play casually, I often forget to do this and can lose focus easily.