I've drawn extensive plans for and built many decks before being a St Louis home inspector, so, I thought a 'what not to overlook when building a deck' or 'common missteps' list could help people build and maintain their decks in a way that helps them enjoy it for as long as they should be able to.
* It's a little thing, but, often, the builder overlooks that the bottom step will be the thickness of the tread too tall, if they don't subtract it from the bottom step in the stringer cut. This usually means that the first step will be over maximum allowable height, and uneven with the rest, making it a trip hazard and general annoyance.
* A trick to stiffining stair railing posts is to add risers if missing, and/or other brace boards under the bottom tread, or near other posts, between stringers, and parallel with tread, stiffining the under side of stairs to reduce stringer twist and wobbling of the post(s).
* Proper connection to the house is, of course important. 3" screws, or even lags are NOT the approved method. Through bolts are, and how often varies. Used what has been called for in plans, and approved by local building authority.
Proper flashing: When water runs down the face of the home and hits the deck, you don't want it coming in, and caulk is not permanent enough here. Flashing from under the siding to the top of the decking or even to top deck joist, is how to keep that water out.
Posts should set on piers that are below the local frost line, and above grade (8" in my area). Posts should also be set on a standoff, to eliminate dirt to wood and concrete to wood contact.
The deck's (usually doubled) band boards should set ON these posts in notches, not screwed, or worse, nailed, like the above photo, to the side of the post. A good looking deck can sometimes be full of deficiencies.
Use approved joist hangers and nails. The nails do a specific job, as they should not rust, and are better than screws in this application. Use both recommended sizes (long and short) in their appropriate holes according to bracket manufacturers specifications. Same for screws, use exterior grade, I like a torx (star) bit.
Add the word 'detail' to your Google photo search for good example plans. Study other decks. What's good, what's bad, what won't last? The old man used to say "Nothing illegal about stealing with your eyes".
This is just the top of the list I most commonly see.
How to cut a stair stringer: How to build a deck: How to stiffen a railing post: common deck building mistakes.