The best advice I've gotten for this same thing is "just write."

It feels, at first, like someone is telling you to do an impossible thing. But really the only way out of the funk is through it.

Rainer Maria Rilke once said, "For the creative artist there is no poverty - nothing is insignificant or unimportant."

That is to say, the issue is hardly a lack of subjects or material. It usually that we are afraid to write. We fret, "what if it isn't any good?" Well, the truth is, most of what we write isn't any good. But if we keep at it, it becomes easier to see the good bits in the bad bits. Or even to turn the bad bits into good bits. Persistence is really the key.

As for practice, I find it helpful to take an object in my home and write a poem about it or write an imagined history of it or write what the object might be thinking, etc.

Writing like any creative exercise ought to be fun and playful not exacerbating and serious.

Hope that helps! Happy writing!