Are you trying to sense or make a psi-ball?
The ability to sense is always there, but must be found first. Everybody has the sense, just like the other five, it's just not used and you've been taught to ignore it all of your life.
Another thing, your subconicous is sort of like the midde-man to everything, so first you need to try and establish communication with it. After that, simple excersises to get your subconcious to display to you the information picked up by the 6th sense is required. Peebrain wrote some great articles on the sub-c; They can be located either on Psipog or now on Psionics Online (I think).
Also, yes, you are doing a good excercise, but you just need to establish that sub-c communication to get more clear and better results.
I am trying to sense psi.
I haven't had much luck, that was the furthest I got. Even then, it wasn't that strong.