Yes, the step back thing is great, for Shockwave...sometimes, the mobs will actually line up, like a "Rockettes" dance troupe! I got into the habit of jumping up and down once or twice, after the Shockwave, as a way of letting my guildie mage friend know I had enough aggro for her to open up on the mobs. We found that was a better way, than relying on the threat meter, or graphic animation to give indications. You may want to do something similar, to let your group know when to start dps...particularly when it's a pug. It will probably be more effective than just typing, "Give me a few secs, to get aggro--k?" I'll just say, "When you see me jump up, go for it!"
As dps, I try to look for visual cues, as a way to know if tank has aggro...like, are the mobs coming together to him, or are they peeling off and heading to the healer?
-"Just like a buzzin' fly, I come into your life, I'll float away, like honey in the sun..."--Tim Buckley