Couching is a useful way to add textured lines to your pieces - and it's fairly easy to create, too!
Couching is worked with two separate lengths of thread: one lies on top of the fabric, and the other anchors it in place.
1. To start, bring your main thread to the front of your fabric - this is the one that will lie on top and create the line. Leave it lying loose on top of your fabric.
2. Take your second thread, and use your non-needle hand to hold your 'main' thread near the line.
3. Bring your second thread to the front just to one side of the line; then bring it to the back on the other side of the line - this should create a tiny anchor stitch for your main thread, just a couple of millimetres wide.
Repeat: lie your main thread on the line; then create a tiny anchor stitch to hold it in place.
To finish your line, bring both threads to the back and secure them in place (a simple knot will do the trick).
The technique for curves is similar - although you may want to place your anchor stitches closer together, to smooth out any sharp angles.