I'd suggest looking up Chase's cresting article. I can't find it right now.
You basically want to slowly deep dive and rise back up and back down, like a wave.
If you deep dive and just stay there, it can keep the mood pretty low. I use deep diving for connecting and use light banter to keep the mood good.
Recently, I was deep diving with this girl, talking about her ex-boyfriend. Her ex-boyfriend killed himself after she turned him down for marriage. We talked about it for a little bit, and I tried to focus on her feelings (as women like to talk about feelings more than details). Imagine if we had just stayed in the deep end? Man, that would have been a pretty awful hour of just deep diving and continually staying in that mood. I thought about making a dark joke ("I hope you don't end up killing me as well"), but I don't think she would have liked it, so instead I switched back to a lighter subject that we had talked about earlier, and I got the mood happy and light again.
You never want to always be in the shallow end or always be in the deep end, I think -- at least for a new girl. I've find out that with my current girlfriend that I almost know every deep-dive thing now, so sometimes, we will just have only a light/shallow conversation, but that's because I already know most of the deep stuff about her.