Don't do anything with your asparagus now. Let it grow as it wants, all summer. It will die off in the fall. We leave it stand all winter, then cut it and burn it right over the bed in the early spring, before you see new shoots coming. I was always told the soot from burning/blackened ground will heat the soil faster and bring the new growth. It also keeps the seeds from the old ferns on the bed to sprout.
The rule of thumb I always heard was to grow it one full season before you harvest, and and
never pick a stalk that's smaller than a pencil. A healthy bed will always have a few new ferns growing in it, and if you don't get it picked, it'll just put more energy into the root to make a healthier bed.
Hope this helps.
Tim