Our industry is fast-paced. You have to be able to turn around ideas quickly. That pressure can block your creativity. To prevent this, you need to constantly train your design muscles. Build a daily routine around creative inspiration, especially if you're feeling stuck on long-term client work where outstanding creativity isn't always part of your job.
For me, this meant incorporating creative inspiration into my daily routine. I use plugins, newsletters, and social media on a daily basis to consume the latest and greatest designs without going into detail or spending time searching for them. While I go after my workday, my mind subconsciously picks up on those design bits, and over time it manifests and enables me to turn around designs quicker. Make sure to save everything that stands out, so nothing ever gets lost.