In my opinion, it is counter-productive to make "using more idioms in what I say" a goal. The poor learner more often than not ends up sounding silly or stilted or both. A more meaningful goal would be "How can I learn to speak simply and precisely?" Simplicity and precision will give you great elegance. If you also have a good accent, then it will be a pleasure to hear you speak.

Listen to people speaking English more often, and understand the context in which the idioms are being used.

'Essential Idioms in English' by Robert J.Dixon (Longman) Is suitable and coherent book.