I had all sorts of problems with writing as a kid, with terrible handwriting and undiagnosed dyslexic issues. To a large degree I retaught myself and now people tell me that I have really good handwriting. I can't write very quickly yet but things are generally much better. I didn't really have a plan, but looking back it was really important to change the way I felt about making marks on paper.
Two things that I think were important:
1 Drawing lots of large abstract shapes by eye (on A3 size paper) particularly drawing straight lines .
2 Practising calligraphy.
In both cases, the fact that I was doing this entirely for myself and nobody else was judging was very important.
As a rule, I don't do a lot of drawing on balloons, but I found copying manga style illustrations to be very helpful. Also the Andrew Loomis books go into more detail than you need, but are very good for judging proportion and are quite beautiful in themselves. Try googling them
http://www.youtube.com/watch?v=9BevsH0jOMA
Two things that I think were important:
1 Drawing lots of large abstract shapes by eye (on A3 size paper) particularly drawing straight lines .
2 Practising calligraphy.
In both cases, the fact that I was doing this entirely for myself and nobody else was judging was very important.
As a rule, I don't do a lot of drawing on balloons, but I found copying manga style illustrations to be very helpful. Also the Andrew Loomis books go into more detail than you need, but are very good for judging proportion and are quite beautiful in themselves. Try googling them
http://www.youtube.com/watch?v=9BevsH0jOMA