In addition
to the two posts above however many posts showed up while I slowly typed, I'd like to add that when I first got an empyrean, the idea of how to best make use of my aftermath seemed really foreign to me. I didn't know... anything, really. But it didn't take long to sort out what was "right" at any given time. Just keep an eye on what you're doing, what you're doing next, and (if you have timers for your buffs, which I totally recommend) how long until your current aftermath wears off.
The two biggest screw ups I dealt with was, for example, seeing that my aftermath wore off, then immediately weaponskilling to restart it. I couldn't tell you how many times I had, for example 170TP that I could have just waited another second for 200 to get level 2. The other problem was also weaponskilling a couple seconds BEFORE it wore off - again, I could have waited just a bit and had instant aftermath again.
Best of luck and have fun!