I build quite a few decks for a living and some of the biggest mistakes people make is not using beams to support the joists, attaching beams and joists to the sides of posts with nails and expecting the nails to support a load. Code in some areas now requires beams to be on top of the posts, not notched. I still notch my posts to support my beams. And lack of diagonal bracing is also very common. I haven't used 5/4 deck bords for at least a dozen years. They shrink too much. Even 2x6's will shrink on you and there is no predicting how much.