What would you consider when preparing a Dj set?
There are many aspects to consider.  Initially having an understanding of the audience and setting, can help in thinking about energy levels (BPMs), and duration.

It is also helpful to plan the direction of the DJ set, ramping from slow BPMs to high ones, perhaps peaking mid-set or just a different series of peaks along the way.

Track selection is key. Having a pre-defined list of potential tracks to play is a great idea.

Another consideration is mixing in key or following a harmonic mixing style for a neat flow.

All of the above require preparation and programming for a well-crafted DJ mix.