Before you write an article, use the free word processing program OpenOffice, which has both a spell checker and word counter. Write your article there and click the spell checker when you are done. Write out your article first, then do any proofreading. Remember the spell checker is just that, it won't correct grammar, punctuation, or sentence structure.

Read it out loud. This will help you pick up on errors that you may skim over when you are reading text on a screen. It will also help you hear where sentences are awkward or confusing.

For essays and shorter pieces, I usually proof them twice - once by reading silently with red pen in hand, and once by reading out loud. I always work with a printed copy that I can make notes on. I also try to get a friend to read longer pieces (especially fiction) in the hopes that a second set of eyes will catch what I miss.

If grammar isn't your strong point and you need to do a lot of writing, I highly recommend taking some time to really learn the rules for commas, semi-colons, and colons. Using punctuation effectively makes a huge difference as to how polished a finished piece is.
As a quick rule: don't use more than two commas in a sentence (unless lists are involved). More than that means you are either using them incorrectly or your sentence is far more complicated than it needs to be.

There are a few ways that I would suggest to proofread your writing. First, tactic is to use the grammar and spell check tools from Microsoft Word. Then, read your working out loud to yourself and you will catch with this activity. Secondly, have two strong writing buddies proofread your work and choose friends who will be honest with you. I would ask two friends who have different writing styles. After your buddies give you their suggestions, I would compare and contrast the two. Analyze carefully, I know it is difficult, but, try to be as impartial as possible. Redraft your work with the suggestions that you keep and then, leave it alone for 24 hours. This is the last round of proofreading the next day. Read your work at this point, time helps to be more fair in judging our own work.