Absolutely separating from the physical body is part of Etheric projection, trying that with astral projection methods only is very nearly impossible. It takes a further discharge of energy from the physical body.
As for astral projection, practically every method considers vibrations, BUT there is a standard method of focusing only on the vibrations. This I do not recommend if you're having trouble projecting. This technique is really for (although not particularly called for) those who have a great deal of experience with it, and are having trouble for a moment to just go ahead and slip into it; this does take a lot of practice to get used to.
What I suggest is using a personal aspect to help you. Have something there to reach for, and that of which sucks you in. Try using a mental image of a portal.
lol This does sound bazaar, but check it out here: http://www.spellsandmagic.com/astral2.html
Read it, love it. It is rather exuberant, but gets you where you need to be or at the least help you.