lucymaylooks like you got a good result! i usually zoom in the image i'm working on and make the selection line one click at the time, that makes it easier to get a smooth line with the lasso tool. another way to get a smooth line is using the path tool

, but that can be a bit tricky if you're not used to it. i start the same way as with the lasso tool, zoom in the image quite a bit. then i make just a few clicks on places where the line bends "dramatically", then i close the path. after that i tweak the path by dragging the little "handles" on each point until the path follows the line in the picture as closely as possible. when the path looks good i go to the paths menu and click "path to selection". - a bit trickier, like i said, but gives nice and smooth selections.