I Think it's good to have a selection of different herbs for all conditions you can, in a range of formats so you can try a little trial and error to find what fits you best. I have currently, in the form of teas, tinctures, glycerites, and infused oils: Mugwort, St Johns wort, Yarrow, Hawthorn, Self-heal, Crampbark, Rosebay Willowherb, Red Clover, Rose petals, Woodbine, White willow, Meadowsweet, Archangel, Herb Robert, Shepherds purse, Dandelion, Bramble leaves... That's as many as I can think of without getting up!
I also use a lot of others just as first aid when we're off in the woods and far away, like Plantain/Ribwort and Burdock.
I started with a BRILLIANT beginners book called Hedgerow Medicine, by Julie Bruton-Seal and Matthew Seal, I'd recomend it as a good 'in', but warn about the addictive quality of stocking your own apothecary!