Every developer should to learn some basic design and front end skills. Employers are increasingly expecting developers to know both front end and back end - especially front end. I've written a bit more about this here, with data to support this claim: quora.com/Computer-Programming-How-does-the-numbe…
Keep in mind that visual design (how something looks) and user experience design (how something) are two different disciplines. Some of the best designed sites, such as Quora, are quite simple visually, but have excellent user experience design.
You can also draw inspiration from other developers' projects on CodePen.
As far as learning design, the best approach is to practice. Free Code Camp will give you experience building more than a dozen front-end focused projects (along with plenty of back-end focused projects). These will give you ample opportunity to apply design concepts.