Interesting topic....

So, first of all, if you use ideas and parts of the old song in your new stuff, you won't be sued for copyright infringement by yourself. I've seen a few of my tunes rip off melody lines and ideas from my earlier writings. No big deal.

You have to simply keep writing. You have to write a lot of bad, average, and almost good songs to get to the "wow this is amazing" songs. The more you write, the better you get at coming up with new ideas. You are under no obligation to post the bad and average songs for others to hear. Trust me, there's notebooks and computer folders filled with song ideas that were originally thought to be "brilliant" that are now collecting dust because....well..... they weren't. Just move on and don't obsess over the stuff you wrote yesterday. That's water under the bridge.... write something else today. Pick a topic and intentionally write about it.

Also, vary the instrument you use to write. If you normally write on the piano, try writing with a guitar.

The best way to break out of the writing rut is to find a co-writer and try doing some collaboration writing. Some of my best songs (in my opinion) have been the ones where another writer and I got together to create something interesting. Look at my songs and check out which ones are collabs. Quite a few are that way. In fact, I'm collabing with a new writer on several new songs currently. Stay tuned for the results.

You can find my music at:
www.herbhartley.com
Add nothing that adds nothing to the music.
You can make excuses or you can make progress but not both.

The magic you are looking for is in the work you are avoiding.