I can't think of a good site, but here are some tips:
Independent Writing Task
- Follow the 5 or 4 paragraph essay structure
- Read the writing prompt carefully and be sure to answer the whole question
- Plan your time: 5 minutes planning, 20 minutes writing, 5 minutes revising
- Write a clear thesis statement at the end of your introduction
- Write clear topic sentences at the beginning of each body paragraph
- Support your topic sentences with facts and examples
- Check your essay for the following problems: spelling, add -s to the verb in simple present if the subject is singular, find and fix fragments, check word forms
For more information on these tips message me or check out my fb page: TOEFLtips