Good to see your interest on vocabulary and making complex sentences. Regrading vocabulary I can suggest you to read newspaper as much as possible. Also, additionally Reader Digest magazine will help you a lot in building vocabulary. Go through the book from the very first page to last and especially you would notice that they concentrate on Vocabulary section where you can learn a lot.
Regarding, complex sentence writing, newspaper reading is the best option but just a friendly reminder, complex sentence is not sweet to hear or read always. Write for your readers, so that they can read your write up and get satisfaction. English writing should be lucid with a flow. But yes, simultaneously I will also say that you have to have solid control over English in respect of making complex sentence too, because that will help you in making easier and simple sentence for your audience.