Strenuously avoid trying to do a spot just made up of current popular sounds - the last thing the scene needs is ANOTHER 'me too' DJ - aim to play stuff that:
A] is DANCEABLE
B] marks you out as different and original (also usually means you have to spend less)
C] offer variation and texture in the spot (smooth transitions between slower stuff and fast peaks, dotted with male/female/instrumentals/older/newer etc etc)
D] Think about what you are playing - decide a musical start point and where you want to finish (I always used to pre-select my key records through a spot - though adjusted it in reaction to the crowd as I went along - and then fill in the gaps like stepping stones, slotting in requests WHEN they fit in musically within the wider spot, rather than immediately playing them - also goes down well because they think you forgot them and then get a pleasant surprise)
E] 'read' the dancefloor - don't go for lowest common denominator records simply to fill it, but recognise what's going down well, this also helps if you clear it (don't panic and just play an automatic floorppacker in reaction - they'll smell blood!)
F] Learn to appear convincingly deaf when someone want you to play Diana Ross
I always looked upon DJing as musical evangelism - 'if you liked that one you already know - you'll love this one you don't know'.
Dave