Please go over your paper with the following in mind. Thanks to PsyDAG for the following:
In the future, 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.)
[You can also either read it aloud to someone else or have someone else read it aloud to you! (The latter works really well!)]
If your reading goes smoothly, that is fine. However, wherever you "stumble" in your reading, other people are likely to have a problem in reading your material. Those "stumbles" indicate areas that need revising.
Once you have made your revisions, repeat the process above. Good papers often require many drafts.
And here are three really good websites that will help, too.
Plus, if you post it here, I'll be glad to proofread it for you.