Before glueing, position the piece where you want it.
Hold it in place & fold some of it back on itself.
Using an eyebrow pencil, mark 2 dots on your scalp & 2 corresponding dots on the underneath of the lace.
Then when you've glued, you just have to match up the dots to get it in the right place.
Once its on, push it down into the glue, using the teeth of a comb rather than your fingers.

Hope this helps.