Yeah the main trick for clean edge highlights are paint consitency, and I usually put a little less water (than usual) for 45° pencils highlights, and a little more (for consitency) on straight lines (like between the armor plates.
Don't hésitate to put 2 or even 3 layers if you want a brighter color.
Another key for a nice looking highlight is the color choice. Most tends to highlight with a color too close to the base (or to mix some base color into the highlight one) and it tends to ruin the effect. if you want this to work, you must go for contrast (for edges). For skin and capes, better blend.
GW paints are a great example for the color choices, as the color couples (layer/highlights) always seems too distant, ubt usually work great when dry.
Also don't forget that you can do a highlight, and if it's to thick thin it down with the base color afterward (wait for it to dry !).
I used this a lot when practicing, to get a cleaner result without re-doing all.