Another good way to practice writing, is to write from memory. So write down your life story in phases, like from 1-8 years old, 9-16 years old, and so on. Looking at an old photo album can also help you remember stuff from long ago. Or ask family members to help you fill in some gaps. Just write it in a interesting way, so others enjoy the read. To be clear, you don't have to write down everything you can remember, just the things you care(d) about. So if you are interested in football, and have been playing this for years, remember how you first started out, and how well you progressed. Or if you are into Sailing, remember the first time you went on a sailing trip and how good that made you feel. Just have fun with it :)
You could also write about your prom night and write in detail what you did that night, or write about the first time you went on a holiday with your loved one, or friends.
Anyway you get the gist of it, so enjoy writing down your fondest memories :)