Push yourself to write each day. I've seen a quote that reads, "You can't edit a blank page," and that's the complete truth. You may not write something worth reading every day, but you'll challenge yourself to improve your writing just by doing the very thing you love to do - write.
This is much more easily said than done, because some writers aren’t to the point in their lives where they write for a living. They have other jobs to make ends meet, and they might not have a ton of spare time each day to write. That’s where quality over quantity comes in. Sometimes the writing you’ll accomplish will feel neither great nor lengthy, but come back to it another day, change some things, or the whole thing. You might look at it differently tomorrow than you see it today. After all, you’re not the same person you were then. A person is constantly changing, being shaped by their experiences, and their writing is shaped by those experiences as well.
My favorite thing to do is sit in a semi-busy public place - think coffee shop atmosphere - and silently observe the people around me. I take inspiration from conversations, from people who come in and leave the place, and just go from there. You can even just sit and write everything that comes to mind. Jot down your random thoughts and ideas, and you can piece them together later. There is no time limit on a piece of writing - aside from deadlines, of course, which I’ve always tended to struggle with. I’m sure that other writers will agree that we, as a whole, tend to procrastinate and put things off until the very last minute. I know the majority of my fellow English majors in college would agree that they’d put off the essays until the last minute. It’s just a writing thing. We might be concerned with perfection, but other times, the inspiration and ideas are just not there.
Break out of your shell, and go outside - yes, I know, as both a bookworm and writer, that’s a difficult task to achieve unless absolutely necessary - and you’ll be surprised at what you accomplish.