The very best thing you can do is start growing your own herbs and use them!
Get a book on herbs; the older the better if you can find one at a used book store or yard sale. The newer books, I've found, steer you away from some of the "old ways".
Most herbs do very well in poor soil. I'd suggest the basics; sage, rosemary, chives, basil, coriander (celantro), savory, and lemon balm. For flowers with medicinal uses try hollyhock, larkspur, lavender, primrose and safflower.
To actually use the herbs, cut them fresh after the morning dew has evaporated. Refer to your book for freezing and drying. Somethings I dry and then grind, some I leave as leaves.
Things to make with herbs: herb vinegars, aromatic baths, fragrant rubbing lotions, catnip pads, incense, moth preventives, and teas.
Aloe vera grows so well on a window sill, I can barely give away the new shoots and more are already growing! Great for any skin condition and burns. Just break the leaf and apply directly.