If nobody is available to proofread your work, you can do this yourself. After writing your material, put it aside for a day — at least several hours. (This breaks mental sets you might have that keep you from noticing problems.) Then read it aloud as if you were reading someone else's work. (Reading aloud slows down your reading, so you are less likely to skip over problems.)
If your reading goes smoothly, that is fine. However, wherever you "stumble" in your reading, other persons are likely to have a problem in reading your material. Those "stumbles" indicate areas that need revising.
Another option, if it is available on your computer, is to have the computer read it to you.
Also, make use of "Spelling and Grammar" under "Tools" in your word processing program.
Once you have made your revisions, repeat the process above. Good papers often require many drafts.