Well there are hundreds if not thousands of different methods when it comes to astral projection. If you've practiced a technique for a while and it hasn't worked for you, try another one.
The following techniques are the most popular and the most effective techniques (and by that, I don't mean they will definitely work for you. You know yourself better than anyone. search different methods and find a technique that feels right to you.)
1)Monroe's technique, by Robert Monroe
2)The rope technique, by Robert Bruce
3)The thirst technique, by Sylvan Muldoon
4)Astral projection via lucid dreaming (which is a very interesting topic)
I recommend you to google these techniques and other techniques, and see what works best for you.