Hello. I don't post that often, but the forum is great for tips. I've been wearing for about 20 years. I'm not sure if this one has been mentioned:

I trim off the excess lace on a new piece in the front (to my desired shape). I then take the plastic, head-shaped mold, that comes with the hairpiece and put it under the piece. I slide it about an inch forward of the hairline. I then trace the shape of the lace hairline exactly and cut off the curved contoured mold. I apply some small pieces of tape to the back of it. Then I stick it on my forehead and use it as a template for applying the glue in the front. It gives a fairly accurate glue job and the piece lays perfectly on the glue.

I saw a similar post a while back about some product for applying makeup accurately that you can buy at a drugstore to do this similarly. I can't recall what it was and this is what I came up with.

Thanks all for the great posts and tips.