It’s best to start labeling your plants while your collection is still small, to avoid a time-consuming ordeal later on. This has the added benefit of allowing you to experiment and adjust which information you put on the labels, as you discover what works best for you.
Don’t get overwhelmed by thinking about labeling your entire collection at once. Make it easy, and fun, to label your plants, by first making only one plant label. That’s right, I said ONE label. Get the supplies, gather the information for one plant, and make one label. If you like it, make a couple more. Gradually, over time, label all of your plants.
A note about display tanks:
You probably won’t want to use plant labels inside of a display tank, such as a terrarium, vivarium, or paludarium, because they will be an eyesore, but you should still track the information about the plants it contains.
One way to track plant information for a display tank, without damaging the aesthetics of the tank, is to create the printed labels for the plants and store them in a ziploc bag or other container. Keep the bag near the tank, but out of sight. I sometimes use masking tape to attach the bag to the back of the tank, or store it underneath a shelf. As you add or remove species, keep the label bag up to date.