If you're a writer or plan to write, please read this.

I refer to this. The entire thing has great information, but you should definitely check out this part in particular. I've lost track of how many stories I've seen that, despite getting the spelling and grammar quite correct everywhere else, did not punctuate the dialogue properly. You can easily avoid this by simply reading the information on dialogue in the linked page, particularly the information on said tags and action tags. So please, if you plan to write or already are writing, familiarize yourself with that information to make sure you get the dialogue punctuation correct. The information is really not complex, and understanding these concepts will get rid of about 20% of your errors.