I get this complaint from at least one student a day when we do our timed writing. I learned this exercise from Natalie Goldberg. Write for five (or ten or fifteen) minutes straight. The only rule is that you don’t ever let your pencil stop. Just write. No censorship.
In my classroom, students write to a prompt. For example, “What makes a good life?” And then they write. This develops a strong writing voice over time.
Of course, as with anything else in life, you must do it regularly and give it 100% each time. You will improve. Yes, you’ll write a lot of crap. But any successful person has created a lot of crap and then a few golden nuggets…