I would search words for an specific subject. Once I take note about the most common then I try to practice using them. For example I write a dialog or a monologue. I also try to use them in my casual conversations with other people

There isn't any universal approach to the problem. Everyone must find their own method.

I think there are a lot of different ways to learn language and the best option is to combine them. Preparing and learning specific vocabulary about a topic is very useful (you can use a fantastic free application called anki to prepare cards and learn new vocabulary). Besides, It's important to read a lot about topics because you enjoy and you are going to enjoy and learn new words. And another important way is to listen to radio or to watch tv.