Take a look at the following to help with the structure and formatting of your writing.
ESL Lounge: A comprehensive website that offers test-prep, listening and reading practice, as well as some grammar exercises. A good place to start is the advanced level exercises, as the intermediate are fairly simple.
Intermediate and Advanced Level
Guide to Grammar and Writing: When you’re in search for specific pages on grammar points and essay structure (down to the sentence level), look no further! You can pick through various pages to find exactly what you need. Some pages also feature quizzes to help you practice what you just learned.
The Purdue Online Writing Lab: To polish your writing abilities, visit the Online Writing Lab (OWL) to learn new writing and style techniques, as well as some grammar points.