Go light handed at first. Feel free to go further in experimenting with flavors. Any smelly edible plant might be useful as a flavoring. Look in your spice and tea rack for possibilities like lemon grass, etc. Mints, Mentha sp.
Mints are probably the most accessible and used flavoring agents for smoking mixtures.
They impart a menthol flavor. This includes Spearmint, Peppermint, and all the numerous ornamental varieties such as Apple Mint, etc. Remember to go light so as not to irritate your lungs and throat. Mugwort Herbaceous Artemisia sp. It's the mug plant used for beer in medieval times.