Visual design is hard to improve because some of it is tacit
Apprentice with, watch, or copy good designers
Collect good design. Look at it closely
Start with something to communicate
Layout, typography, and colour are incredibly important
Use systems to make coherent design
Good design is easier if you use less stuff
Learn whatever good visual designers have written down
Learn rules you can safely follow
Learn techniques to polish your design
Learn why good design looks good
Your personal style will develop naturally