I think I am a fairly savy flower gardener (until I meet others with way more knowledge, which immediately humbles me). I also think I am pretty good at finding my way around the computer until I discover something new and then think, wow, what else can I learn? So this is what I have learned.
native plants: incorporate them into my garden because 1. They are lower maintenance ( less watering, less fertilizing ) 2. They promote a healthier environment for wildlife who depend on them. It's an interesting read if you click on the link. And I am in camp "conventional-appearance", which means I still want a landscaped look to my garden but am trying to use native plants instead of mass produced industrial plants that are pushed by nurseries or contractors.
Things every gardener may want to know:
plant zones - The most basic of helpful things to learn is your "zone". Especially if you order plants online. My zone is 7a, you can even discover your ecoregion if you want to get fancy. I am in Ecoregion 66j - Broad Basins...something I can throw out there when talking to plant enthusiasts, lol
soil types - Again, very basic information here which makes a huge difference in whether or not a plant does well. I am not a big "amender", I prefer to go with what is there and work in that direction. ( another reason to use native plants ) My soil type is not listed here, it's just a basic guideline, so you may have to research yours further. ( I'm lucky to have a loamy soil )
Soil Moisture - Want to get serious? Look into your soil moisture, mine is Mesic, mainly cause I grow in a shaded wooded area alongside a creek.
sunlight definitions - This can be a tricky one and you may need to study the area to determine what your sunlight is. For my woodland garden I am "partial shade, dappled shade to full shade".
Micro climates - Now take everything you learned from above and adjust it, or throw it out the window if you have micro climates, because you can grow plants not in your zone etc. It may be warmer or colder, wetter or drier, or more or less prone to frosts...so yeah, it's a game changer.
Lots more to talk about, tools, pesticides, insects, identifying poisonous plants....but this gets you started in the right direction.