I learn Mandarin and while the vocabulary, tones and characters take lots of practice, the sentence structure requires experience.
To step me through the vocab, speech and writing in congenial company, I use the social network LiveMocha. I don’t find the lessons particularly well designed, but the community is friendly, and it is easy to find a study buddy who will guide you in return for your help in their English studies.
Sentence structure requires another approach. If I were in China, I would read and hear sentences every day. But in the middle of England, without a Mandarin speaker in earshot, I need a way to read regularly.
For this I signed up to service from Transparent Language that sends me a sentence a day. I receive a new word every day in a sentence in pinyin (our script) and I can click through to see the Chinese characters and hear the pronunciation. Sadly that is in Flash and we can’t copy and paste the characters into Google Translate but the essential purpose is achieved. I am regularly being exposed to normal sentence structures.
Zuó tiān xià le dà yǔ
Yesterday it rained heavily
Literally: Yester day under(past tense) big rain
This sentence was quite fortuitous. We have an unusually heavy wet spell at the moment in the UK. The sentence also shows why this additional homework is so useful to me. Though the sentence uses common characters and is much simpler than an English sentence, it is not at all like English. Experience is simply as important as learning examples.
I recommend the service highly as a supplement to your efforts to learn Mandarin.
May 2017: I use mobile apps now. Not as sociable but contemporary apps (just five years later) check my pronounciation.