There are numerous resources depending on what type of writing you are interested in.
My suggestion would be to start with Purdue Owl, which has great general tips as well as in-depth explanations of different types of writing.
The UNC Writing Center has handouts on everything from outlining to descriptions of different types of writing (abstracts, book reviews, etc.)
For particular grammar exercises, EnglishPage.com has exercises to help improve subject-verb agreement, tenses, prepositions, and other grammatical constructs.
I would also highly recommend visiting the Writing & Reading Hotspot. The writing coaches there can help guide you through the writing process for a specific assignment and writing in general. The Lone Star tutoring website has links to all the colleges and their hours.
No appointment is necessary at the LSC-University Park location Monday through Friday. Saturdays require a prior appointment.
