Here are some photos to help you figure out the best place to have the head table and the DJ booth.
 Here is a great example of a good layout. The head table is directly in front of the DJ booth so the DJ can see the head table and know when they are about to make a toast or speech so they can turn down the music accordingly. The guest tables are also on the side of the DJ booth so they can have table conversations without having to talk over the music.

This room is almost set up perfect. They have two buffet tables, to help ease the time the guest have to wait. They have the card box on the opposite end of the room, away from the exits. But look at the DJ booth. It almost looks like an afterthought. It is so far away from the dance floor plus during dinner music only half of the guest will be able to hear the speeches if they are using the DJs equipment due the location of booth.

Another bad location for the DJ. How are they going to entertain your wedding guests from WAY over there?

Here is a very simple layout of a room. They DJ is able to see the whole head table. Everyone in the wedding party has easy access to the dance floor when it is time for important dances like the father/daughter dance.

The location of the Dj is one part of a very big puzzle to help make you reception memorable. They help control the flow of the evening. Keep them in a corner or away from the dance floor and your DJ will have a harder time performing his/her duties as a master of ceremonies.