The best advice is to calm the body and mind and allow things to occur naturally. As Aleister Crowley said "Sit still. Stop thinking. Shut up. Get out." That succinctly summarises the method I use.
Astral projection is actually a natural occurrence and by-product of meditation, however, there are techniques for people who struggle early on, but ultimately it is and will become a natural experience if you do the necessary meditative work.
I recommend the following and can only speak for myself:
Lie down in savasana, or what is known as the corpse pose, and visualise a light which has the intent to relax the tension in the body. Start at your feet and move this light upwards until every bit of tension you feel is gone. Cycle the energy at least 3 times, and really do make sure you are completely relaxed- people often forget the back, jaw, face, and scalp.
After this you will be breathing deeper, I now recommend regularising your breathing. The fourfold breath is perhaps the most simple. This will aid in relaxation, building energy, and going into a light trance.
Breathe in for a count of four, hold for a count of four, breathe out for a count of eight, hold for a count of four, and repeat. Do this until it feels right, that is to say, gauge when you have reached a state of trance and can feel the energy of the body, this may take time.
Once you get here you are going to form a body from the astral light, which is a fancy way of saying your are going to visualise an energetic double emerging from your body and standing at your side. There are a couple of ways to do this, you can simply already visualise the body standing, you can visualise this energetic double coinciding with your physical body and split apart and stand up, or you can visualise energy poring out from the solar plexus or heart chakra and forming the double.
Once this is sufficiently done, you then need to transfer your consciousness and seat of awareness into the double. There is no way to describe how to do this, it just comes naturally. The trick is to simply use the imagination and will together to be in the double, to experience sensations as if you were the double until eventually you are the double. If you do use the chakra outpouring into the double you can use that connection as a method of transferring your consciousness, I personally don't use that visualisation, but I know it can help others.
This is the hardest step, as I say, astral projection is quite natural, forcing it to occur is obviously going to be hard to do at first.
Opening the astral eyes will be hard at first, but with time and practice it can be done.
When you can walk around the room, you are then able to proclaim you can etherically project, which is to say you can explore the energetic backbone of the physical plane. To astral project, that is explore the next plane up so to speak and other portions of spiritual consciousness you visualise yourself rising through the ceiling, then throught the sky, higher and higher until eventually you come to a landscape.
Don't take this as literally meaning you flow through space, it is merely one of many hand visualisations which shakes up the mind and allows for astral projection. When you reach another plane you may see and experience things, you may ask for a guide. After a few experiments you may want to learn how to control your journeys to explore specific planes, or you may not. That is a completely different discussion.