If you want to get started TODAY with expressing yourself through improvisation here is a very simple exercise you can try
Go to your piano or keyboard and hold down an F. While holding down that F, play any other white note you want in any combination.
When you do this you will be improvising in the Lydian mode, which is just a variant of the Major scale that sounds bright and uplifting.
Try one note at a time against the bass note and see how each one makes you feel.
Find your favorite ones and play them in different combinations.
Hey, play them all at once!
Just go nuts and have fun. (Remember, it’s only music!)
If you want to get a little more fancy try your hand at the Blues Scale. Hold down a low C and with your right-hand experiment with the notes C, Eb, F, F#, G, and Bb. This is a tried and true method for improvisers at ALL levels. It may sound a little weird to you at first, but just have fun with it!