We are the music makers - producers?

Try using a reference track and copying the structure bar for bar. Do this a few times and you'll get used to it.

As @Regal says

I also find it useful to commit to audio quickly. If you're working in MIDI it's tempting to keep on tinkering.

Easier said than done but try and finish everything you start. Quality comes through quantity. Work fast, use any old sample and make it fit, try not to think it all has to be perfect.

So many ‘Sketches’, so few finished songs.
Anyone else suffering with this?
Anyone got any advice or tips to get things finished?

Feels like producers that don't relate to this are the exception.

For me, breaking up writing, recording, and mixing into separate sessions is important for me as without it I'll spend the first hour eqing a Kick and loose all my momentum.

Lately I've also been putting time limits on how long I have to write each part and that's also helped me a lot.

I've also very recently tried @Regal and @EB 's suggestions with success. It took me far too long to get over myself and try mimicking another track, but I learned a ton when I finally did and it even sparked some new ideas.