When I first starting learning herbalism, I didn't know a whole lot. I knew about cooking herbs and spices, those great illegal ones, and a few others from a herbie friend of mine (http://www.wanderinghen.com). The more I began to read about them and their qualities, the more I began to understand them. I highly encourage all that use herbs to become intimate with what they are burning or eating or smoking. Not just for safety, but to develop that mystical connection. That intimacy that they came first and we should respect them and the land they grow on.
A few exercises:
1. Burn a little bit of each herb, plant, spice, or oil you have, all by it's self. Right down it's characteristics and how it makes you feel. For example, I think orris root smells a lot like burnt marshmallows, so I put a little in my incense when I feel a nice "outdoorsy" undertone is needed.
2. Know what's dangerous or poisionous and stay away from it! Just before you aren't smoking a plant doesn't mean that you can breathe around it's incense smoke either!
3. When compounding, write down combinations that you really like and the amounts that you used. That way, you can always come back and make it later.
4. Obtain your plants in a way that is respectful and ecofriendly. More on that later.