When You can't seem to get going
We all get stuck sometimes, but maybe you have a deadline. Or maybe you just can't get past it. I'm listing what I've tried and what has worked for me at least once. I hope it helps you too.
Take a Break
I still find it hard to think of creativity as something you need a break from, but if it isn't striking, sometimes it just isn't there. Stepping away is a great way to refresh. Listen to some music. Try a different genre; for me, I find classical, jazz, or basic piano to trigger a lot of ideas.
Change your environment
When I'm sitting at my desk, it's convenient for working. I have good monitors, a good screen: a generally proper setup. This is great most of the time, but sometimes getting away from my desk, and sitting elsewhere even if at home, can help brighten the mood. Creativity requires inspiration, and a stale environment can be a creativity killer.
You can also switch things around in your workspace. This may not be all that possible, but even changing a few things around on the wall, or moving around some knick-knacks could help.
Try learning a new genre or plugin
I'm not saying you have to master it, but if you have trouble just "stepping away" like I do, it can be a good way to keep engaged without the pressure of coming up with a top-notch production.
Flipping through Presets
I've come up with many a melody just by flipping through presets. Sometimes, the sound itself can inspire a melody, or just the change of sound can keep the creative juices flowing. One hand on the music keyboard, the other on the computer keyboard (or mouse).
Start with a common tune like "Twinkle Twinkle Little Star" or "Jingle Bells"
This gets something written. Then get everything else laid out, and come back to it. Move some notes around while you are working.
Use a different DAW
This can be tricky, but could be helpful to some. I found that, similar to learning a new genre, I wasn't focused on coming up with a good production, but just to test things out. I ended up exporting my MIDI for the real work, but it got me going.
Limit yourself
I don't know where I heard this, but I've heard it a few times. Limit yourself to a few notes with one hand, one plugin/synth.
Recreate a track you like
You may go all the way, or may get to a point where you get inspired and go off on your own. Maybe you only choose certain elements that you'll try to replicate, and leave the rest for your own experimentation and creativity.