It takes practice to get there. You set up your circle as usual. But once you are set up you need to chant or hum or what ever you wish, but repeat it until the energy has built beyond what you can hold, repeat it until it has filled your circle. It should feel like it is just your mind; your spirit, walking hand in hand with deity. Nothing else is there. It should be as if you exist in that one thought of why you are there to start with. This could be spell working or invoking deity. But being able to reach the astral plane is a must for ritual magick.
And with practice you will get to a point where it will come almost like second nature, and you won�t need a circle to reach it; but it is easier within a circle.
