We did this in stages, gluing our figurines one day and then filling the jars with water and glue after the decoration inside had time to set up. To make it more visible, we mounted a bottle cap on top of our lid (which served as the base). Vitamin bottle caps work great for this. So, once your decoration is in there and you've filled your jar with water and added glitter, how much glycerin? Well, it depends on how slowly you want your glitter "snow" to fall. The more glycerin the slower the snowfall. I think we used about a quarter teaspoon. Experiment with this. Some sites suggest mineral water instead of glycerin but we found that it made the water cloudy. Some sites called for waterproof glue. We tried that. The figurine fell off its stand with one small tap. Regular old glue gun glue worked like a charm.
One of the globes we used aquarium sealant to make sure our lid stayed on. The other two though, again, good old glue gun glue did the trick. You want to fill your jar as full as possible so you don't wind up with an air bubble at the top. But hey, if you get a bubble, put a decoration on the top and no one will be the wiser. This makes a great project to do with girlfriends or older children. We had a wonderful time together doing this. And our snow globes turned out great. The picture doesn't do them justice. (I didn't inherit the photography gene either!)