Read more and listen more. Try to imitate expressions of native speakers.

A lot of practice communicating with other people

Read and listen by yourself, speak and write with a teacher.

Practice a lot. Talking to people and reading a lot exposes you to new vocabulary and speaking trains your mind to come up with the vocabulary you have learnt. The more you speak, the faster your mind will be able to process the vocabulary. Also if you dont have the vocabulary to express the idea you have in mind, try to rephrase it. Use synonyms or explain the idea instead of using one single word. This is normal during the learning phase of a new language, so don't feel ashamed of it or be shy about it. Eventually your vocabulary will improve.

watch movies:)