One more I think worth adding, that I’m stealing from Mike Monteiro, is the ability to effectively present / sell your work.

It’s one thing to create a solid piece of work that fulfills the requirements of a project, and it’s a whole other thing to convince others of that fact.

I’ve worked with a lot of talented designers that weren’t strong presenters and it’s quite a liability. Poor presentation skills can result in the loss of confidence from the client or the team, unnecessary rework (or flat out rejection), and ultimately a weaker final product.

All of those issues cost time and money.

Luckily, just like every skill you mentioned, it’s something that can be improved on — but just like every skill it takes reps.

Of all the skills a team could invest in, I’d argue presenting has one of the highest ROI’s.

https://medium.com/@monteiro/13-ways-designers-screw-up-client-presentations-51aaee11e28c#.82zuetc68