You could also try tightlining with a gel liner or regular pencil liner
Ive just bought a Bobbi Brown eyeliner brush and long wear black eyeliner gel, im hoping to be able to do this tightlining technique with these 2 products but to be honest it looks really difficult :-/
You picked two excellent products! BB has the very best gel liner on the market, IMO, and I was only able to start doing my eyeliner better once I started using it (I wore some today, in fact).
Like others have suggested, I would def. check out YouTube tutorials (there is a thread around here on good YouTube makeup videos) and/or ask the person who sold you the gel liner for some practice tips. Finally, you might want to consider starting off with a shortened (travel) version of the Bobbi Brown eyeliner brush. This might give you more control - I tried this and found it helpful.