suicide, you need to use the pen tool, you`ll get much smoother lines.
Just follow the lines with the pen tool. Then take the brush tool, set the brush to 1 pixel or 2 depending on how thick you want the line. Don`t do anything else with the brush tool. Then go to pen tool again, do right mouse click, select - stroke path - in the window that pops up you choose to stroke as brush.
now the selected line is black.
To take the pen tool line away, you do right mouse, and delete path. Now you have a smooth black line if you`ve done it right.