If you could give only one piece of advice to a new grower

Keep it clean. Wipe up spilled water, vacuum regularly (don't forget screened intakes etc), sanitize everything between grows.
I even dip everything in bleach solution that I bring into the condo that I've bought at hydro/gardening stores.
Oh and drain off excess liquid from your saucers.
Cannabis doesn't like wet feet.
I'm 53 and have been growing for 6 months.

Best advice is keep it about the passion not distribution it's a beautiful process and there's no rush enjoy every stage and learn everything you can keep detailed notes

If you are going to use more than one room (Highly recommended) realize that on average you will need to dedicate 4 square floor-space for each flowering lady and one square foot for veggers. I know the numbers are crude at the plant-to-plant level, but they are close overall. My flowring room is 8 X 8 = 64 square feet. My veg room is half my laundry room and is 3 X 5 feet. Most growers start out thinking the vegging/flowering floor space to be equal. So learn the easy way and figure in more flowering space early and save later headaches.. Been there, done that.

Good luck, BigSteve.

Been growing for 3 weeks... Best advice would be to not shortcut the research phase by asking such an open-ended question : o )

Log it or it never happened
35+ years

Relax, find your center. Be the plant.

Perseverance

Don't waste your money on bottled nutes with pretty labels. Waste your money on hookers and blow.

Don't come back here in 5 weeks and ask "How much longer?" or "How much do you think I'll harvest?" or "Should I flicker the lights on and off for the last two days while standing on one leg in a bucket of molasses?"

Definitely don't ask about pissing on your plants. That's just bad JUJU.

6 years non stop.

Learn to water a plant correctly. Probably one of the most common cause's of problems.
During the last week of flower foliar feed with 2 cups of Sasquatch semen. Preferably from a left handed one. You'll have the stickiest bud ever. Bring jack links, happy hunting