Best way to calm your mind is through practice. Start out with guided meditation (such as listening to one of Kelly Howell's guided meditaton). These types of meditation will help you find focus and ground yourself. With practice you won't need to listen to someone in order to stay focused.
Once you can sit through guided meditation, you can go to the next phase. Try practicing with your breath. Count how long your inhales & exhales are. Remind yourself to breath. Eventually, your mind will stop counting and become silent.
Last type of practice is finding an object to focus on and silent the mind. Anytime you feel a thought, acknowledge it and say it can wait til later. Then thank yourself and begin focusing again on your selected object.
Do meditation when you won't be disturbed for a dedicated amount of time (5minutes for beginners and add additional 5 more minutes as you feel comfortable)
Try different times in the day to find when you are least mentally rambally from stress.
Practice mini visualization when awake (can be anywhere and anytime). Sort of like asking yourself "Am I awake?" But, in this case you will be saying "Am I an astral being?" Think of what you would want to expect when you astral project.