Getting the levers level, drop bar.
So here's what I do, it's time consuming and I hate it.
1. Two levels, one on seat tube and one on seat. This is to confirm that laying a level across the seat actually is level due to inconsistent pads or something.
2. Level across the seat and long level across the hoods. Adjust accordingly. This works well on my old trainer and old bikes but is not compatible with thru axle and I never use a trainer otherwise, so I'm not getting a new one.
3. Try to find point to point measurements to reassure myself. This never helps.
4. Eyeball it and call it good.
5. Wrap the handlebars and ride. Realize it's wrong.
6. Carefully unwrap the bars without tearing the tape and repeat steps 1-5 in any order.
7. Admit defeat, ride. We're all a little lopsided anyway.
Also important, the marks in the stem clamp region of the stem are occasionally not the dead center. I feel like there should be a Park Tool for centering bars.
With the advent of flared bars and long levers, I haven't had any luck running a straight edge to the lever tips. Come to think of it, I've never had any luck with that trick.