First off, yourself and most people know how these days to burn a cd with music they like or make a playlist on I-Tunes and even hook their computer to a stereo for entertainment. Sometimes although you might need more sound for more people. Sometimes you might not want to have to worry with the duty or you don't trust that guy that shows up every party and holds the cd player hostage.
Sometimes there is a need for a DJ. Whether you know what you're doing or are clueless to the whole process.
Let me suggest a few things.

The first question you need to ask of all DJs is....Are they dependable?
I have performed in nearly 3000 performances in 16 years. I have never had an equipment malfunction that has hindered my performance. Never have I been late or not shown up. I have always arrived at the earliest I could to setup and make sure all equipment is working. After each show, I pack up quietly and quickly to make departure easy.

Most DJs specialize in one type of music or event and do not do both karaoke & play music.
In my 16 years of performances I have had the opportunity to do every type of party multiple times.
(with the exception of a bar mitzvah. Still looking for my first.)
From a small sweet 16 to the largest wedding. I have the experience and the equipment to cover the event.
I have not only a 30 year knowledge of music, recording and studio work.
I have a vast collection of music. Added with the power of the internet makes the amount of songs limitless to pick from.
I also am setup to do digital karaoke. That means no skips, stutters on anything that could ruin your performance.
With the internet also almost every karaoke song is at my fingertips.

The next question to ask of the DJ is if he is entertaining.
I cannot speak for any other DJ than myself. Some never talk. Some say the wrong things and others never shut up!
It's your event and whatever you need the host to be I will be. I practice and write out any announcements or speech that needs to be said. I have wireless & multiple mics for others to speak. I can be invisible in the background or I can force everyone to do the chicken dance. Most clients hire me sight & performance unseen. I have never disappointed and can give references for any type of event you may require.

And Finally...Why should anyone hire DJ SkyHigh?
I show up. I am prepared. I am polite, accommodating and professional.
I make all the DJs hate me because they are not me.