If you have been learning a foreign language for a certain length of time, the day will come when you won’t be able to find any learning materials which aren’t below your level. However, at the same time, you won’t be perfectly fluent yet. I was at this stage in German for a long time. Although I could use the language well, I still believed that my knowledge of and fluency in German could be better.
Sentence mining is not only useful for a beginner in a language, it can also be very helpful in getting intermediate and advanced learners further ahead. The best way to do it is to read materials which are aimed at native speakers of the language. The materials can be about any subject that interests you. While you’re reading, collect any useful sentences and make a course out of them in a similar way as described in my article ”How to Learn a Foreign Language for Free Using Word Frequency Lists.” The criteria that you use to determine which sentences can bring you closer to fluency are up to you. Personally, I collect sentences which either contain a new word, a new way of phrasing a sentence, or which contain a fact that I want to remember.
The best thing about this method is that it’s entirely based on your interests, so you’re more than likely to stick with it. You can do a web search using the foreign terms and find a wealth of places to sentence mine. Wikipedia is one of my favorite places to sentence mine, as are the free online books at Lernhelfer.de. This also helps you to pick up specialized words and terms in the target language.