Like anything learning SQL takes practise. Hands On SQL is one great way to get that practise. You also need to be challenged and try solving problems different ways.
It's easy to think once you have learnt a few skills that you can do anything, and while you maybe able to, without being challenged and learning new ways to solve problems you wont grow.
SQL Murder Mystery and SQL Police Department are both fun exercises with large data sets that require you to use sql selects to investigate a crime. They are great practise at getting familiar with a new data set and interrogating it.