One of the interesting things about teaching composition is that it requires students to get used to exploring sounds, options and ultimately dealing with the fact that initially a lot of what they try isn’t going to work straight away.
There is a criteria you can set, you can work within parameters and music theory and other knowledge can certainly help in making choices that are suitable, but with that knowledge is also the willingness to take the rulebook and throw it away as that leads to innovation and originality.
Some students are so fearful of this, that it requires a Herculean effort to put anything down. To create, we need to get used to putting down bad ideas and then thrashing through them.
Almost always, there is potential to find something worthwhile amidst the ideas that are laid down, that is where thrashing can happen. What is worth keeping? What can we develop here? Will this work better if we get rid of this part or save it for later? What if we try this or that approach? How can we make this better? A myriad of questions to ask and plenty of creative possibilities.
Being open to the creative possibility is key and it comes when we give ourselves an environment where we can thrash through what we have without any judgement from the outside world. Just you and the work, and maybe some trusted people to advise you along the way.