Similarly, I know many student art directors who approached assignments by thinking about layouts way before they had a concept.
Granted, both approaches may lead you into some interesting areas and shouldn’t be discounted. Just make sure they’re not standard operating procedure.
Personally, my best ideas come when my partner and I separate ourselves from the rest of the agency (either in a coffee shop or a closed conference room), and talk. And keep talking. As soon as two minutes have passed without either of us saying a word, we've stopped working as a team. You've got to keep talking.
Yeah, you'll stray off into travel stories and "Did you see what Chiat/Day just did?" tangents, which is totally fine. (I used to swap recipes with my last partner.) Just make sure you course correct frequently and get back to talking about the brief.
If you're talking, you're thinking. If you're thinking, the ideas will come.