Here is a very practical tip to relax your mind and suppress random thoughts while preforming any kind of meditation including yoga:
Relax your tongue. Let it just hang in there without any pressure. Once you tongue is relaxed, relax all the muscles of your face, including your eyes.
If you do it right you will find it very difficult to speak in your mind or see any random images.
Relaxed body is the key to right meditation – #FeelHearty