That blank piece of paper can be a bit daunting - but remember, it's only paper!
Open your sketchbook, set yourself a time to draw or paint (you might even want to set an alarm on your phone), pick a subject and just go for it! With or without a reference image is fine.
Then, when you're done, put a date on that page and let it be.
Make this a regular practice and you'll see the improvement as you fill your book!