The Rockowitz Writing Center at Hunter College is a general resource for help with academic writing. They are located on the 7th floor of the Library and generally open from 10am-7pm Monday-Thursday.
The Online Writing Lab (OWL) at Purdue is an excellent resource to help you understand and use the various popular citation guides used in scholarly work (MLA, APA, Chicago, etc.). Each type of reference generally requires special handling, and many examples can be found on this website to ensure that your work uses proper scholarly standards.
Grammerly is a powerful grammar and spell-checking tool. It offers top-rate corrections and diagnoses--well beyond what is available in most word processors (it can even find instances where you have correctly spelled the word but are using the wrong form--e.g., too/to, bare/bare, your/you're, etc.). There is a premium version that is probably worth the money if you plan to make a profession of writing, but even the free version can be very helpful.