Learn to step away and trust in synchronicities in the creative process. It's taken me a long time to develop this trust, and it's a lesson I often forget. But, increasingly, it's becoming a critical and trusted part of my writing process.
When I first started writing, and this applies especially but not exclusively to my attempts at fiction, I noticed that when I finished the first draft of a piece, and then stepped away for a day or two the oddest things would occur. And they tended to occur at the most inopportune moments - while eating dinner, while my wife was asking me something, while washing dishes, while showering, while going for a walk, while waiting for my dentist appointment - little inspirations would simply popinto my brain. These inspirations often appeared completely out of the blue. Other times, the thought would be triggered by something new that I saw or read.
Whatever the cause, these little nuggets of inspiration from aetherwould materialize when the Muse appeared and whispered into my ear: entire plot changes, surprise twists, ideas to make the characters deeper and more human. Sometime entire vignettes for describing the setting more vividly appeared in my mind.
At first I thought I was simply "lucky" to have thought of such improvements, and I would scramble to go work on the piece before forgetting the new inspired idea. But after noticing that this happens each and every time I write, I've learned to trust the process of inviting the Muse of synchronicity to do her job. The Muse may be a superstition, and perhaps this is simply the workings of my own brain, but it's a superstition that works for my process and therefore, it is useful.
So now, I do the following: I create a rough draft (usually unbelievably rough) and I put it away. For the next few days to about a week or so, I simply trust that inspired ideas are going to appear. And appear they do.
Sometimes I consider, and then reject them. Sometimes, I play with them in my head and think through how they could work. Sometimes, I just know that it's a great idea and will improve the work (these are the best). I've also learned that it's not necessary to write the idea down immediately. I like to let my mind work on it a bit. If I don't remember it in a few hours, it probably wasn't that great of an idea. I've also learned though, that I usually do need to jot a high level reminder down within about a day or so.
So, as I go through my day, if I have an idea I want to add to my current piece, I just note it on my phone or iPad and move on. Just a few simple words to jog my memory when I finally return to the writing desk.
I like to think of "inspiration" not as just as the original idea, but more as a quantity of quality that one puts into their art. In other words, some pieces have only a small amount inspiration and some have quite a lot. By trusting this process, I'm able to "add" inspiration in small and large quantities by going back to the draft and adding the accumulated quanta of inspiration I've had in the intervening days.
So, if you're looking to create work that is deeper, and that contains more inspiration, I'd recommend giving this process a go. [1] Lay down your first attempt at the work. And then just put it away for a few days. Let things simmer in your subconscious. You'll be surprised by the moments of inspiration that happen and they will lead you to large leaps of improvement in the work.