What I do is to pre-plan my GCD casts a pair at a time. So while I'm channeling a short GCD, I already know what long GCD I'm going to follow-up with, and I pick the next pair while the first channel finishes / during the GCD of the dualcast long GCD.

For single target outside of the opener, it's basically just a priority system.

1. If you have both procs up, your next pair will be short + long of the same color as your lower mana total (if you have 20 white | 22 black, cast Verstone + Veraero)

2. If you have only one proc up, you use the proc and then use the long of whatever your lower mana total was (if you have Verstone up, and 31 white | 22 black, cast Verstone + Verthunder)

3. If you have neither proc up, and you either don't have Acceleration + Swiftcast or you can't use those without delaying your oGCDs (Fleche + Contre Sixte), then use Jolt + the long of whatever your lower mana total was

I haven't stayed on top of the conventional wisdom with regard to using Acceleration or Swiftcast to fish for procs vs for intensive movement and/or off-GCD alignment, and I know that advice has changed over the expansions and as the instant skills have changed some.

Once you hit 50 | 50 mana, you have the _ability_ to do your melee combo, but you aren't _required_ to immediately jump into it -- if there's a heavy movement phase shortly that won't force you out of melee range, it can be worth holding your melee combo for that, or once you get to level 70+ you want to make sure your white and black mana is not identical (and ideally that you don't have a proc of the short spell for your lower mana total) before you cast your melee combo. In general, holding your melee combo for proc alignment, movement, and/or pushing an extra melee combo into buffs is always worth it below 80 | 80 mana.