Hello, this is my first post.
I thought I would offer some advice. I have been composing since the age of 8 and playing the piano since I was 3 yrs. old.
My Mom - a classically trained pianist - gave me some advice that I never followed until two years ago. She told me to run my scales everyday. Since following her advice not only has my playing improved, but my composing is so much stronger because I am able to improvise to a greater level - I wish I had listened to her years ago.
Also, practice with simple songs - practice making them your own - writing extensions to the piece, playing them in different ways with different techniques, etc.
One more thing, learn all the classical pieces you can! Many of my compositions were inspired from Mozart, Bach and Beethoven. Just playing these pieces will give you new ideas AND train your hands to flow a certain way as you play!
FYI – I must warn you..
I have no formal training, I've never even taken a piano lesson - but I find exercises such as these really help me think out of the box and help find my signature.
Good Luck, Artgirl