I love narrow raised beds so I only have to improve the soil in a small area. Then the soil is so rich that I can plant veggies close enough to crowd out weeds.
Your soil improvement might be an ongoing project for a few years, but eventually you'll get it so rich and aerated and well-draining that all it needs is compost 1-2 times per year, and some mulch. Until then, tilling and even (gasp) some chemical fertilizer might not be bad things. But many organic advocates do fine with fish and seaweed emulsions and lots of compost.
I dig up the soil in pathways that surround each bed and shovel it back on top of the bed, screening out rocks and roots. I mix in compost, sand, grit, compost, bark fines, compost, manure and compost at the same time. You can't add too much compost when starting a bed!
I dig down as far as 12 or more inches, and build the bed up to a total of 16" (my walls are made of paving stones from 8" to 16" tall). For me, drainage is a problem and soil is pure clay, so root-zone depth is a good thing. Also, I can't squat or kneel and even bending is tiring, so by lowering the pathway and raising the soil surface, I put my hands that much closer to ground level.
The pathways can be around 18" wide, or wider if you want a wheel barrow, or narrower if you are steady on your feet and space is at a premium.
Other people will say "What a waste of energy!" and just layer 12" of compost and compost-makings on top of whatever soil they have, without even turning it up with pick and garden fork! The they grow for a few years in the compost layer, while worms and watering mellows the underlying soil FOR them.
I guess I just like digging and turning the clay and dirt and rocks until they become soil.. Maybe there are some mole genes in my family history.
