Hey Philipp, welcome to the forums.
Lot’s of questions. The most important piece of advice I can give you for a first gig is: Be in the NOW and ENJOY it. Count on things going wrong (stuff usually does, even for 37yr experienced guy like me) and also on the crowd not really caring that much (I have done stuff like start/stop the wrong track, pull the wrong fader and such and survived those nights).
As for organising your collection, finding a few (3-4) tracks that work well together and putting them in a mini-playlist is a good idea. It takes some of the what’s next stress out of playing.
In theory anything danceable is playable in my opinion, but it clearly depends on the venue and the crowd. Play deep house at a hardstyle party might not go down well or playing 70s disco all night at an 18-year old’s birthday party. You get the idea.
It’s a good idea to spend some time in advance checking out what are good points to start mixing in and out of a track. You don’t have to start at the beginning and you don’t have to play all the way to the end. Setting cue points to the mix in point is good practice. Also make sure your tracks are correctly beatgridded so that a set cue point snaps to the beat.
While you don’t have to play song out to their full length, I personally don’t like to cut tracks too short. I usually calculate 20 tracks to an hour, giving an average of 3 minutes a track. I know 30 tracks an hour is also a number that people use. All very personal to your style of DJ-ing of course.
Since you know music, you’ll understand that things happen on the first downbeats (of 4 bars). In (most) dance music, things are also built in blocks (=8 bars = 32 beats). So getting things to happen on the first downbeat of an 8 bar block/section is also helpful.
Finally, harmonic compatibility is something to watch for. While it’s perfectly doable to play around with tracks that don’t harmonically fit, it is helpful to know which tracks ARE in the same harmonic key. Free software like KeyFinder or it’s paid (and better) counterpart Mixed in Key can help you figure out the key automatically and tag your tracks so the key is available in your DJ software. Some DJ software has keyfinding ability, but those are generally less than KeyFinder (and most definitely less than MiK).
Another thing that is good practice is to prepare your set. This does not mean making a set playlist and just slugging through it all night, but this does mean picking tunes that you think you might play that night (if you have mini=playlist those would be the small blocks you’d pick). A good rule of thumb is to bring about 2 times the amount of music you will need (4 hour set at 20 tracks an hour = 80 tracks, so you’d need at least 160 tracks) and have a plan b – list with another 80 or so tracks. Don’t fall in the trap of bringing everything you own and trying to figure out what to play on the night itself. If you have more experience and a very deep and intimate knowledge of your entire collection, this is not a big problem. But in your first gigs, taking away sources of stress is a good thing.
As for playing slow (tempo or low energy?) intro tracks that build up to a grand finale, those of course you can use, but it’s important where you use them. You want to build from a lower tempo/energy section in your set to a high tempo/energy section and then slow it down a bit again. This will create some sort of “wave” through your entire set.
Always look at the people to see how they react to the things you play and base your decisions of what’s next on them.
Good luck.
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