I tend to make herbal blends/powders a whole lot in my practice. There are many ways to do such a thing, but here's a basic way that I use often.
If you aren't sure on the sort of blend you want to create, you can always research the meanings of each herb to find out the meaning. So after listing all the herbs you want in the powder, you may find them in a dried form at the grocery store in the kitchen spices aisle, or just a section where cooking ingredients would be found.
Now you will want to grab your mortar and pestle, and(if you own one) a coffee grinder. A coffee grinder is great for making finer powders and grinding the resistant herbs. I would also gather a mixing bowl (I use a beautiful glass bowl, but you can use whatever feels right to you). After you've grabbed all your things, along with your herbs, you can start creating your powder.
Generally, I would grind each herb individually with my mortar and pestle and visualize the property of the herb flowing into it as I made it into a powder. You can also place it in a coffee grinder and visualize the same thing, but only hold the button down a few seconds to prevent getting a burnt kind of smell, or just to avoid burning the powder. Do this with each and every herb, taking time with it as you go.
After they are all made into a powder, then you may place them all into your bowl, and stir clockwise. Make sure everything is well combined and a nice uniform color. This is a great time to put all of the energies and your intention into the powder.
Finally, you may store it in a baggie, a jar, or any other sort of container. You may use your final powder as a loose incense, a wash, combined with an oil to anoint candles, cone incenses, in a candle (placed into the molten wax), in a mojo bag, or in various other magickal creations.
Please have fun and be creative!
SOURCES:
My Brain
http://www.youtube.com/watch?v=RP2uXOIgCuM (A great source for wanting to know how to make incense on a budget!)