Two things on my list of failures: 1) Not mulching and 2) turning my soil annually. I previously believed that a vegetable garden should have beautiful black dirt between neat rows of plants. I believed that the soil needed to be turned each spring and "refreshed" or aerated, with peat moss and/or compost added. Maybe a package of this or that soil enhancer. What ended up happening is a big fail: my soil dried out and weeds took over. By the end of the summer I hated my garden. The few tomato plants that survived were ragged and worn out champions, split fruit, falling over, etc.
Now I'm not turning my soil, and I'm covering with newspaper or cardboard mulch and then a layer of old rotten leaves, wood chips or straw.
My goal is now learning how to let nature be nature and how to observe and learn how things grow and interact.