Breathing together means setting your bodies at a similar pace. You can get a lot of information about your partner's state of mind as you pay attention to their breathing: quick and shallow means nervous or anxious; long and deep means relaxed. Try to guide each other to breathing deeply and slowly together, synchronizing your heart rates, and possibly even your brain waves.
Pace the Session
Good impact play starts with good pacing. You don't want to hit super hard at first; you need to build up blood flow and endorphins in your partner. If you spent some time breathing together, you'll be more attuned to your partner's reactions, which means you'll be better able to increase the intensity at the right time.
Every person is different, but here's how it goes for me. If the session is too light, I just kind of get silent and a little bit bored; if it's too much, I'm screaming and trying really hard to move out of the way. The perfect intensity is somewhere in between, where it's hard enough that I vocalize, but not hard enough that my breathing becomes shallow and my screams sharper.
Good pacing is basically the secret to long sessions, too. If you can warm up and intensify incrementally, you can manage to hit your bottom pretty hard after a while.
Check-in With Your Partner
As with all BDSM play, checking in regularly with your bottom ensures that you're keeping it fun for them (and yourself). Checking in also serves to tell your partner that you're still paying attention to them, and not lost in your own space. It makes bottoms feel safe, heard, and connected.
None of this is new to experienced players, of course. A specific focus on connection can transform your play sessions from purely physical activities to meaningful moments with your partners. In the best of times, it can even become spiritual and transcendent.