Focus on your breathing. Make sure you're in a quiet place free of distractions. Try to go through 10 reps 10 times... with enough practice it will come. Even Zen masters can have trouble meditating from time to time. Don't get frustrated.
if you're new your mind will chatter a lot, just breath and don't focus on your thoughts. you could also try focusing on a metronome or clock, playing music [no lyrics] or a guided meditation, perhaps try drinking some type of calming tea to get yourself more relaxed. also, try meditating in the same spot every day so your mind will start to associate it with meditation and relaxation. your mind is always thinking, so it will take a while before you hit that tranquil moment most people think of when they think of meditation.
i was reading a book where at one point the author went to a 2 week meditation retreat. the first day or two all he could hear was the song 'Barbie Girl' on repeat [a song he hated] then he focused on the guy sitting next to him and he began to resent the man, by day 5 his thoughts went inward and he suddenly remembered every hurtful thing he had ever said and done. he brought each of these things up to the councillors and they told him it's normal, your brain is working though detractions to get to buried emotions until you finally reach your center.
meditation is about relaxing and letting your thoughts flow, you could start with just a few minutes a day, or try and push past these random thoughts, but some days you'll find it easy to tune out while others your mind won't settle. its part of meditation, go with it.
What you are describing is not unusual. Many people experience this same thing. There is a link on my profile to an article about meditation. It is slightly different than just trying to quiet your mind. Please feel free to read it and use it if you like.