Here’s a useful tip I came across the other day on a new language-related blog – carry a notebook and pencil with you at all times and make a note of things you’d like to say but don’t know how to. Then find out how to say them later by looking them up or asking friends who speak the language you’re learning.
Another good tip is to ask learners of your target language who are at a more advanced level than you to explain things you don’t understand. People who have studied a language as adults are probably able to explain grammar and usage better than native speakers. If you grow up speaking a language, you develop instincts about how to use words, but cannot necessarily explain to others why you use them in a particular way or order – it just feels right to you.
That second point certainly rings true for me – when friends who are studying English ask me to explain why a particular word is used in one place but not another, or ask questions about grammar, I try to work out the answers, if I don’t know them, but often just tell them that that’s the way we say things, and I don’t know why.