BE CAREFUL. It kills any plant it comes into contact with. Use 1 part vinegar, 1 tablespoon soap, and 1 part water.
Hemerocallis will sometimes set proliferations. Once these little plants show up on a scape, and a root begins to emerge, remove the proliferation, and either plant it in a small container, keeping it moist but not wet, or put the proliferation into water with the crown above the water line. You will get a new little plant that may eventually reward you with blooms identical to the plant it was taken from.
Some indoor and outdoor plants can be rooted directly in soil.
Talk to your neighbors and see which vegetables they will be planting. You can then plan to grow different plants, and all of the neighbors can share the bounty of their harvests with each other.
A used dryer sheet in the bottom of a pot will help keep the soil from falling out of the drainage holes.
Recycle small containers to start seeds in. One could use cleaned yogurt or gelatin cups, water bottles with the tops cut off, egg cartons, and the list could go on.
Indoor plants enjoy a shower every once in a while.
If you use polymer crystals in a container, it's best to hydrate them before adding them to the soil. This way you won't end up hydrating them with your first watering and having soil rise up, over, and out of your container.
Be sure to label your seeds as soon as you harvest them.
Trade seeds -- either ones you have extra of, or newly harvested.
Trade plants. Plants often need to be divided, and many gardeners could benefit from the divisions you don't need.
Save seeds. Many seeds grow very easily even when you just sprinkle them where you would like.
To easily get seeds from Centaurea cyanus (Bachelor button), roll the spent and dried flower head with a small amount of pressure between the top half inch of your forefinger and thumb. The seeds will fall right out.
When you get your new plant home and are ready to plant, snip off any bloom that may have come with the plant. The energy will go to establishing the plant instead of maintaining the bloom.