Here is Geshe Tenzin Tenphel’s detailed description of how to do prostrations:
It is not absolutely necessary to perform physical prostrations. If you can’t do them, you can generate faith in your mind, but if you do them, you should ensure that you do them properly. The palms should be put together with the thumbs tucked inwards. This is related to Avalokiteshvara’s two hands at his heart, which hold a wish-fulfilling gem. This is just one way to do it. In fact, in different Buddhist traditions, there are different ways to place the hands when doing prostrations.
With the palms together, we first touch the crown of the head, then the throat, then the heart, or center of the chest. In this way we create the causes to obtain the buddha’s holy body, speech, and mind. The feet should be placed together, the body upright, and the head inclined slightly downwards. When you go down and place your hands on the ground, the feet should be kept in their starting position, and touch your forehead to the ground. Come up quickly, without staying on the ground. The fingers should be kept together, not splayed apart, and you should not lift yourself up by making fists. When we prostrate, we touch the forehead to the ground, which is to show respect to the objects to whom we prostrate: we are putting ourselves in a lower position as a sign of respect. The reason to stand up quickly is to symbolize that we do not stay in samsara for a long time. If we have the fingers far apart, we create the cause to be born as a goose, a duck, and so forth with webbed feet. If we make a fist as we come up, we create the cause to be reborn as a horse, donkey, or other animals with hoofed feet. If we stay on the ground for a long time, we create the cause to stay in samsara for a long time. If you are a bodhisattva, perhaps you do not mind staying in samsara for a long time! Of course, here when we say that you create the causes to stay in samsara for a long time, that means staying in samsara for a long time under the influence of afflictions. Also don’t swing your arms too much, otherwise you might kill bugs in the air; keep your arms near your sides in a dignified way. If you are not careful, you may create negativites. If you know how to do prostrations, there are many benefits; if you don’t know how to do them, there are many drawbacks, so we should be attentive and careful when we do them. Do not think it is difficult.
When we go down on the ground while doing long prostrations, there is a description of the body being like a tree falling to the ground. If we do long prostrations, it doesn’t make a difference if we slide while we do it, or if we place our hands on the ground in steps. It depends on the mind of regret in relation to our negative actions. This mind of regret can manifest very strongly, and a sign of that is that you slide on the ground when you do long prostrations. The essential point is to place your entire body flat on the ground and generate this wish to be protected, making the request,“Please protect me, take care of me!” When we do prostrations, in addition to prostrating physically, in our mind we should have strong faith, and we should recite various words with our speech; in this way, prostrations become complete in terms of body, speech, and mind.
source: Geshe Tenzin Tenphel, FPMT Masters Program Ornament of Clear Realizations unpublished transcript May 23, 2008 teaching