Removing the need for the score

Here I can tell you a trick that helps starting getting rid of a score.

Improvisers do not usually need a score, may be sometimes they have just one small piece of paper where someone wrote a melody on which to improvise.

So a nice and rewarding exercice is to do the following: take a score that for you is simple (so you can focus better on what you do) and just read the left hand from the score while improvising the right hand (or the pedals if you are at the organ).

I think the best way to do this is to do a copy of the score and then remove the right hand (in XXI century this is easily done by scanning - image editing - printing; anyway also XX century way is ok...). In this way you are not distracted by the original version.

Start with some "chords composition", where you have a chord for every number of bars (like a mozart Rondò for example) and then try with more counterpoint...

This is just in advice: you should make it work for yourself.

You can take also an heavy metal guitar riff and work on it: this sounds impressive on the organ. I did this with Metallica's Battery: just try!