In my view, the best way to learning English idioms (fixed expressions) is by topics with explanations of meaning, examples of usage and subsequent exercises. Practising idioms can be done through exercises in listening comprehension, speaking, reading and writing. I suggest the following sequence of learning English idioms (5-10 idioms per lesson).
1. Read clear precise meanings of idioms with usage examples in several realistic sentences in a good thematic dictionary of English idioms.
2. Make up your own sentences for using idioms in real life situations.
3. Do ready-made exercises from text books in idioms practice. Exercises in idioms practice can include dialogues, narrations (telling stories), thematic texts, questions and answers with idioms in various situations, discussions, talking points and expressing opinions and views on real life topics and issues.
The most comprehensive aids for learning English idioms are dictionaries of English idioms that contain thematic arrangement of idioms.
Below is the list of the most important dictionaries of English idioms.
1. Longman Idioms Dictionary (over 6,000 idioms : choose the right idiom with the unique Idiom Activator)
2. Longman American Idioms Dictionary (over 4,000 idioms)
3. Cambridge International Dictionary of Idioms (7,000 idioms : with 15 topic classification of idioms)
4. Collins Cobuild Dictionary of Idioms (6,000 idiom expressions : This has a thematic index of idioms)
5. Oxford Dictionary of Idioms (over 5,000 idioms with a thematic index of idioms)
6. Oxford Dictionary of English Idioms (volumes 1, 2)
7. Oxford Idioms Dictionary for Learners of English (10,000 idioms)
8. NTC's Dictionary of Everyday American English Expressions (over 7,000 expressions presented according to topic and situation)
9. NTC's Thematic Dictionary of American Idioms (900 thematic headings)
The English language is rich in idioms and although it is possible to converse correctly in non-idiomatic English, a student with only a superficial knowledge of English idioms will find himself (or herself) at a serious disadvantage in his (her) reading and even more so when he (she) takes part in discussions and debates. Ready-made copious usage sentences of English idioms taken from real life offer guidance on the most effective way to use them. The English Idiom Dictionaries listed by me in this post provide clear idiom usage explanations and several realistic idiom usage sentences. Many native English speakers, especially when they converse among themselves use idioms, informal colloquial expressions and slang.