I think one thing every gardener needs to learn is basic plant propagation. With a little bit of plant propagation knowledge and some courage, you can quickly double, triple, really multiply your plant collection and have some plants left over to share.
Some plants do the propagation for you! They self sow themselves all over the place. You can just dig up the seedlings and move them all around to other parts of your garden as you wish. Or share them with friends, with the appropriate caution about self-sowing. My "wonderful" variegated artemesia self sows very nicely. However, I'm not of a mind to share it with anyone, because it is too prolific in self-sowing.
However, I have another variegated leaf plant that self sows that I do like to see the seedlings of and share them with others. It's a false sunflower, Heliopsis helianthoides 'Loraine Sunshine'. I don't have a current picture, so here's a link if you want to see it. I think it is a real beauty of a plant! The only problem I've had with it is that the 1st year I got it, the rabbits were biting off some of the stems, and leaving them laying on the ground! (They didn't even have the decency to eat what they chewed off!)
Other plants help you along with propagation by sending up new shoots and basically getting bigger and bigger, so all you need to do is dig them up, divide them into smaller clumps and replant them. There is where the "courage" part helps for some gardeners. They get a little squeamish about cutting into the plant and dividing it up. But trust me, the plant will recover and in many cases respond with even more vigorous new growth. You can divide daylilies, peonies, hostas, asters, and many other perennials this way. I have my best success doing this in the spring before there is too much growth, and I always use a good sharp knife. In fact, I purchased a knife that is slightly curved with a serrated edge for just this purpose. You don't have to go to this extent, I just like to buy gardening tools. (If you are new to the blog, check out my hoe collection... there's a link on the right!)
For other plants, you need a little more knowledge to coax them a bit into propagating by rooting cuttings, grafting, etc. But, it is well worth the time to study up on the subject and learn how to do some basic propagation!
Oh, and seeds. Don't forget to try some seeds.
(The picture above has nothing to do with this topic, it's just a little garden ornament I have by my front steps. Oh, and it's raining (a lot) again this evening, so not much progess made in the garden!)