Graphic Design Resources

I've been in ID for years now but was never formally trained - just figured it out as I went. Other companies I worked for didn't have the budget for certification and neither did I. I'm confident in my ability to create clear, engaging content. What I'm less confident in is my ability to "make it pretty." I rely heavily on the available formats and templates, which isn't a bad thing, but I want to grow beyond that. How does someone decide on a splash of color here, a swoop there, creative transitions or animations? 

I'd appreciate any tips, tricks, resources for improving my graphic design skills in course creation, because I feel a bit stuck at the moment.