Personally I stick to on-page for new websites and then worry about off page a little while down the line. I just do the basics first:
Titles and descriptions, image alts, keep content long and descriptive, more text is almost always the way to go. Clear and easy to use navigation – proper color coding and site structure.
Then say a month or 2 down the line I begin to worry about link acquisition and anything else. A great tool to help you with your on page optimization would be seocert.net/site-analyzer.php. I am sure there are a few more like it around the web but I prefer this one.