If I am not sure how things should be laid out I just sketch it on graph paper or on my tablet, I consider each square of the graph to be 10 pixels or what ever suits and have at it. 10 or 15 minutes will generally be enough to go through many revisions and leave me with map to follow, 5 or 10 minutes of typing and it is done. After that tweaks are just changing a few numbers and the results are essentially instant since no compile time and you can see the results with a command from your editor.

Wish also has an interactive mode, not point and click but results are instant, great for learning Tk. No idea if it can work with tkinter though.