Nobody is perfect when writing. Even the most experienced writers and editors make mistakes. It is an axiom of publishing that you cannot proofread and edit yourself. That is why there are so many typographical, grammatical, and other mistakes on blogs and private websites. Most people don’t take the time to proofread or edit themselves. The best way to overcome this is to have an experienced editor/proofreader read your words prior to publishing them.
Failing that, there is an abundance of free or inexpensive software available that will read your documents aloud to you. Have your computer read your word processing document, and listen to what it is saying (the second part might be easier said than done). It is critical to listen to every word the computer says, as missing even a syllable means you might let a typographical or grammatical error remain in your writing. See how many problems you correct with software before you publish.