Not so much a “partying mindset” as such, but recording your mixes on a little portable recorder (or software) I’ve found makes me “bother” a bit more about what I’m up to in an empty club, when sometimes you are tempted to get a bit lazy. Kind of puts a bit of pressure on, especially if you you record the whole night with other DJs too and share it with them after (which is why I prefer the recorder) as you know other people are going to listen to it at some point.
Also regarding the time as a practice session and experimenting with different techniques or effects that you might not “risk” during peak times is another way to go too.
Finally “bringing the party energy” is not always the appropriate thing to do – the supporting, slow build-up set seems to be a bit of a forgotten art these days… people used to even specialize in playing warm-up sets of excellent often multi genre music that wasn’t party music at all as a kind of foundation for the rest of the night.