Detail is often your enemy. Some artstyles can do it, but a lot of the time, especially for a comic, high detailed backgrounds are distracting and noisey and get in the way. They take far too long and your reader won't notice and they will distract from what's important.
However, for establishing shots, and even sometimes general background, I take example from one of my favourite artists and concept artists Yocky, and particularly, this absolutely fantastic time lapse of how they real life photos to become gorgeous landscapes.
https://twitter.com/Yockyy/status/1257436431695437824
But, if you're going to follow that method, either make sure your photos are taken by you, or free to use and edit (so many people forget that part) stock photos. Beyond that, I like to look at artists who inspire me. I also enjoy using Flowscape to create 3d spaces, it's not the most expensive program in the world and while it has quite the learning curve, it can create some nice backgrounds and references for fantasy especially.