Thoughts are like clouds. Sometimes they roll in softly and other times they blow in quickly, but you have control over them with your conscious mind. Whether you're meditating or not you can practice saying "clear" if a thought comes in that you don't want. At first, you may be saying clear a lot, but you don't want to use terms like block, erase or anything that would inhibit your thoughts capacity to present ideas, so you just want to clear the ones you don't want.

If you don't have time to meditate during the day then try just before bed. The idea here is to clear your mind completely. No images, no scenes, that's a different type of meditation and you're most likely wanting to go to sleep. So, use "clear" until your mind is trained to slowly bring in thoughts that you can control better. Also, if you're doing this before bed tells yourself "relax" softly in your mind or "calm". Repeat these softly to yourself.

Now if you want to do standard meditations that's a different discussion.