I distinguish between inspiration and motivation. I
always keep a notebook with me. And when an idea for a particular script I'm working on or thinking about strikes me, I dash a note about it. Inspiration is the part you can't force. Now it doesn't mean that the idea will make it into the script, but sometimes re-reading it later inspires other thoughts.
For motivation, you need to set aside a block of time. It may mean eating at the table with your laptop open or sitting on the porch for 30-45 minutes each day. It needs to be away from audio (radio) and visual (television) distractions. I understand how physical and/or mental exhaustion can zap motivation. What I remind myself is that I can write at least 1-2 pages of a script (about one scene) in an hour. If I do more, that's awesome but I commit to at least one page. If you do that, you will clear a short (20-30 pages) in a month's time. But if you do this routinely, something kicks in and you actually write four or more pages in a sitting. Some days, you forget about TV. And if you truly are drained, at least commit to reading your inspiration notebook and adding to it. Sometimes I'll take that time to flesh out a character's backstory or description. Doing research (wiki, youtube, internet search engines, etc.) can count for my inspiration.
Sometimes, in my script drafts, I will paste in notes so it's right in my script for ready review. Could be backstory or character descriptions. Obviously when you finish writing the script, you remove it but it keeps it available for review when I'm writing. For me, the script draft is a flexible storage document that I build on. Once I'm ready to share it, I clean it up to meet professional standards.
Professional writing requires discipline. Freelance writing can be equally demanding. If you are writing for your own production, it often helps to set basic goals. While others may argue I'm too lenient with just 30-45 minutes or 1-2 pages per day, I've found they are doable and realistic for many writers who struggle with multiple commitments (job, family, etc.).
Post it where you can see it:
Code:
-- Everyday an hour before my TV show or during dinner,
I'll write 1-2 pages on my script.
OR
-- If I really can't write, I will re-read my inspiration notebook
and perhaps add a bit to a character, scene, location.
OR
-- I will cut-n-paste interesting ideas I find into my draft script
to be incorporated later.
As long as you commit to some action, you continue to move forward. Motivation comes from the Latin
motivus meaning "moving". Good luck!