<p>One of the things I'm confused about is comma placement, what exactly is wrong with the sentence:
Sam enjoys crossword puzzles, he works on one every day.
?</p>
<p>I think it should be a semicolon since two independent clauses cannot be separated only by a comma.</p>
<p>It could be a semi-colon or a period.</p>
<p>definetely a semicolon or a period. I would suggest to read the rules in barron's book. really cool explanations about this kind of things. :)</p>