Mistakes are how you learn!! The #1 mistake is not having tried gardening earlier because of worrying about making a mistake!I assume the blogger will post lots of answers from different gardens. I will see if I can get a link to share.
That said, I have found that the most important things in getting a large harvest are making sure you have (1) regular irrigation, (2) appropriate soil, and (3) at least 4 hours of midday sun. Also think about growing what you like to eat and including a variety of plants.
The most important thing in enjoying gardening is to just get into the soil and don’t worry about failure. Enjoy the feel of the soil, the sunlight, the opportunity for hard work, the beauty of the plants. See how things work out and then ask others, read, and learn about what you want to do next year.
What do you think is the #1 mistake that new gardeners make?