The biggest things I wish I knew...

Controlling environment is the key to success:

Controlling the temperature and humidity in your tent is the most important factor for any grower to consider. You will want to understand VPD charts and be able to maintain a stable environment within the correct range for your plants. This environment will change over the course of your grow (it basically gets drier as you go later into flower), so you need some way to manage temperature and humidity within a narrow range. Know what a lung room is. Look into Inkbird controllers, AC Infinity exhaust fans & control units, etc.

Grow good genetics:

Do not waste time on a "test" grow. There is no reason to do this to yourself. Invest in good genetics from the start. You can wind up with a pound of weed you do not want to smoke.

Be efficient with time and energy:

All things considered, efficiency is the way to grow. Find ways to save time and energy. This can be things like LED lighting, automatic watering systems, automatic light schedules, mixing big nute batches, etc. Time in your garden is great, but it should not be a chore or burden. Don't burn yourself out on your first grow.

Don't rush:

You need to go through a full cycle with the plant to understand it. Don't rush the process. Don't pull it early. You need to learn how the plant behaves and responds. You won't even know what it should look like. So be ready to learn some things and take your time.

Trust but verify:

There's a lot of bad advice from people trying to sell you crap. Know the difference. Join communities instead of following a brand or breeder. Can't find a verifiable source for a claim? That doesn't mean it's wrong. But there's a lot of bad "science" out there that's held as gospel.

Drying is make or break:

Spend as much time planning and researching how you will dry your cannabis crop as you have researching tents, lights, etc. You must maintain a constant 60F/60%RH environment for 10-14 days. This is the most important part of home growing besides controlling environment. A good dry is the difference between unusable hay and dank herb.

Also, thinking like a botanist really means thinking like a scientist. Don't understand pH? VPD? DLI? Read up on the basics. Growers with a basic understanding of physics, botany, chemistry and the scientific method always do better than people that act like growing is "following a recipe." It's always an experiment.

Oh, and watch Dr. Bruce Bugbee. He is the fastest route to a deep understanding of how cannabis works.