Practice. You don't have to have a project in mind. Just practice :)
This is how I started training myself. I got a book with 300 motif patterns and I started crocheting the motifs in it.
Well, a lot of them. I crocheted around a hundred (so far). In the process, I was able to refine my crocheting and get "cleaner" outputs.
It's actually nice to have a motif collection. It's better to have the actual crocheted sample of a motif than the image in the book as reference. If you're a serious crocheter, having a collection like this can give you tons of ideas and inspiration for projects!
I had to put a tag on each of them so I could track the motifs I have done so far. I still have a long way to go! If I'm determined to make at least one a day, I can actually make all the motifs in the book before the year ends. Let's see!