Punctuation is important for meaning. During a lesson once, I came across a study where they gave people a sentence to punctuate. It was “A woman without her man is nothing”.
They found, the women tended to punctuuate the sentence: “Woman, without her, man is nothing.”
Men tended to put it, “A woman without her man, is nothing”.
Two very different meanings and a lot of husbands sleeping on the couch. Still, it goes to show you how important punctuation is. I found a free online grammar checker – http://www.grammarly.com/ and some basic rules to follow http://www.yourdictionary.com/grammar-rules/punctuation-rules-help.html.
The best advice I ever had though was simple. Read the sentence out loud. If you pause to take a breath, put in a comma. If you stop and think of a new idea – full stop.