Spellcheck, Read over for grammar, Use paragraphs and topic sentences.
I have been reading over some written work, and since it is the end of the semester and papers are due:
I find that most students shower and look at a mirror before they go out on a date or before a job interview. Every time you write you are being interviewed by the reader. So clean up the obvious problems (see below), and reread what you have written.
a. Be sure to spellcheck. Red underlining in Word. (Note that proper names are usually indicated by italics.) Blue underlining indicates something seems wrong: too when you mean to. If you have written material as part of a website, it pays to check out that material by pasting it into a blank Word document to see if you have any obvious problems.
b. Read aloud what you have written. Native speakers of a language usually speak grammatically, so if you read it out loud you will find things that don't sound right. Word uses green underlining for grammatical problems, but also for two spaces between words and other mistakes. If English is not your native language, the green underlining may be helpful, but it is not always reliable.
If you have typos, usually green underlining should help.
c. it's/its, to/too/two, there/their . . . are frequently confused by native speakers. Lots of other such homonyms. This is much like being color blind, and wearing mismatched clothing.
d. Make sure your written work has sensible paragraphs, each paragraph beginning with a (topic) sentence that summarizes the paragraph. (This is too rigid a prescription, but at least it is a start.)