I use a mini lipbrush from the Bodyshop for my fluidlines. I've tried other things, but keep going back to this one. Though sometimes I naughtily borrow my best friend's Bobbi Brown liner brush, it's very good too....
The technique I use for "wings":-
1. Line the main part of the lid first.
2. Look yourself square in the face in the mirror and decide where you want the far end of your "wingtip" to sit. Then use your brush, pencil or liquid e/l applicator to draw a little "dot" where the wing should stop at each side.
3. Look at yourself again squarely in the mirror and try to work out whether the dots are at the same place on each side. Wipe out and redo until they look as even as possible. Trust me - it's easier to do this with a little "dot" than a wonky line!
4. Now that your guide "dots" look right, use your liner to join the end of your main eyelid liner to the dot in one stroke. It should be easier to keep the line right with the dot in place to guide you.
hTH!