Hello Decorators,

Here are some tricks, I hope you'll find helpful:

1. Use as many shortcuts as possible (time saver in any application).
   Record and use actions for the most frequent operations (e.g. stroke line (path), fill in selection, etc.)
2. Use Pen Tool. Needs mastering for good results, but the final lines can by perfectly smooth when skillfully operating handles and corner points. Sometimes, it just needs just a few clicks to obtain complicated shapes, as compared to Polygonal Lasso Tool, where you need click on and on to obtain sooth curved lines (which in fact are combined of short straight sections, sometimes visible on final decoration.
3. Stroke lines (paths) - see point 2 above. Use hard round brush with the size corresponding to the line width.
4. Use Custom Shape Tool. Make your own base of the most typical decorations/shapes.
5. After making selection, click right mouse button to see all available options, i.e. Free transform, or press Ctrl+T and
   click right mouse button to see available option for Free transform.
6. Instead of making transformation after copying an object to a new window, just duplicate the layer and make transformation on the duplicated layer. You can duplicate just only the selection if needed.

Optional. Work on resized (enlarged x2/x3, for instance ) version, when done change to the final size. Working on larger images may be easier, depending on your individual preferences.

Regards and happy drawing 😃.

P.S.
Some of the general suggestions may also be addressed to Gimp users.