Plenty of articles on the blog and threads here on the forums about building sets. But no matter how many times you read about moods, reading crowds, creating a vibe, etx, there is only one real way of learning this stuff:
DO IT!
The only sensible thing to do is use the time you have to make mini-playlists (3-5 tracks) that go well together and that you know how to transition to and from. Make sure you have several playlists with various genres, bpm-ranges and energy levels. Now you can pick a playlist and start playing in the knowledge that you are comfortable mixing these tracks (little stress that way). Watch the crowd, do they like what you are doing? Play a few more tracks from the same playlist. No reaction? Switch to another playlist after 3 tracks in the old playlist. This way you have a kind of LEGO system, you can take the building block that YOU feel should come next, look at the reaction of the crowd and then decide where to go next.
As Rizki said, it’s Utopia to think you will keep everyone’s attention on the dancefloor all of the time. Individual people will come and go on the dancefloor and sometimes there is a general “walk-off”, often after you’ve played a particularly good and high energy part of your set which had everybody dancing hard. If you play one single tracks that is even slightly sub-par to the previous tracks, people will take that as a cue to go and rest, drink, sit, talk, flirt, whatever. Don’t let that upset you, adapt your music (play a few tracks with a lower energy level before slowly building up the energy again).