I believe there are two skills EVERYBODY should work on regardless of their title or role: writing and sales.
I think writing is the ultimate self challenge. It is a way for you to argue with yourself and work out your ideas so that other people can understand them. When you sit there looking at a page (or screen) you think of how your writing will be perceived which I think leads to better ideas. Most people have expertise in some area. Start writing your thoughts down even if you have no plans to publish them.
Everyone works in sales, they may just not know it. At some point, we all will need to convince someone to hire us, promote us, or support our ideas and visions. That’s sales! I love sales books because at their base, they are all about problem solving and understanding other people’s motivations.
If you can clearly and coherently communicate how you can solve someone’s problem, you will be a force to be reckoned with.