You have to look at everything (at the same time). As you imply, when the plane's wingtips face you, that's often the most difficult to discern what corrections are needed. Wingtip up or down still requires rudder to correct in that condition.

In general, assuming the plane is close, looking at the tail when canopy or belly faces you, and wingtips when sides face you is a good place to start.

Now I really just "stare" at the whole plane and that works for me.

I recall "cheating" a little to help the plane rotate faster through the side facing transitions by giving left roll input to minimize my (error) corrections at first.

As BarracudaHockey says, getting a foamie is a good way to get comfortable. It helps to be close to the plane (without being afraid of it) so your depth perception can be used as well as the visual cues I mentioned. Down on the deck and close will speed this.

And a simulator of course.