Centering, that is to concentrate yourself upon you, is one of the most basic techniques in Magick. If you don't have enough discipline and self-awareness to do this exercise, then there isn't much hope for you to advance further in the Magickal world.
There are several techniques to do it, choose your favourite and later you can make the required adjustments to make it more suitable for your work (you can mix different techniques). I began doing it 7 years ago, I still practice it and yet sometimes it still surprises me. Before describing the technique I use, please notice that nothing's set in stone in terms of physical positions, exercises timing/duration, order of exercises, etc. Everything is subjective to each individual, but the discipline to begin and persevere on this venture is the only requirement for new experimenters.
This technique was created by I. Regardie, and is divided in 3 steps. The first one is just to lay down, completely motionless, just feeling your own body, and avoid (or block) all thoughts that may arise. In the beginning it's very hard to "not think", to think about absolutely nothing, just to feel your body. If you can manage to tough it out 5 seconds, be happy for that, but you'll need to practice much more for longer time spans. The way I started doing it, I was shooting for at least 10 minutes, and trying to reach 30 minutes without thinking. Give yourself at least one month to reach your objective, but you may need more time (like I needed then).
When you reach 30 minutes (or more if you can), even if you're "not-thinking" isn't 100% perfect, you can move on to the next step; relaxing your body while "motionless". This can be done by imagining your blood flow through all of your body, starting in the head and ending in your feet, and your blood is the relaxing tool of your body as you go scanning with detail through all of your body and relaxing what you feel - and this includes eyes, ears, mouth, tongue, neck, hands, genitals - all that you can "grab". This will take probably more than 30 minutes, but for me the best approach is to not keep track of the time, just try to concentrate on your body, bit by bit, going gradually over each body part until you finish your whole body.
The third step is simply quiet relaxation. Get a clock that ticks or a metronome, and during 10 minutes you establish your inhaling and exhaling time by the ticking. For instance you take 4 seconds inhaling and 4 seconds exhaling. You choose your own rhythm, a metronome can be much more eclectic in establishing your timings. With this procedure you begin to realize how your breathing works, and to control it. The breathing can also be a handy way to forget your thoughts, just concentrate on your breathing, don't think of nothing, just feel the inhales and exhales. This can bring healthy feelings into your body, and since I started (for quite some time now), I choose my own rhythm without the help of a metronome to keep it, because I really like the feeling it brings.
Some final notes: a book where you write a daily report about your performance, besides stimulating your awareness, can be very helpful when you try to perceive what are the differences since the time you first started, how you evolved, and your current activities.
As a tool Centering can be very useful during stressful situations, first you react by being aware of your body and then controlling the way you are reacting to external situations. This can block external influences upon yourself, and you become much more aware of your actions and reactions, basically you begin to control yourself.
This is a work in progress, try to be disciplined and do it at least once a day at the beginning, but don't forget that most people already spend more time watching dumb TV shows than looking at themselves (maybe you aren't just another TV sheep), so don't expect immediate results.
And Magickal techniques like Visualization, Astral projection, Magick rituals - all are based on centering one self. You cannot become proficient at any more advanced Magickal techniques if you don't master Centering. At the very least, it can only improve your self-control.