Always wear gloves when dealing with black walnuts. Walnut hulls contain one of the longest-lasting natural dyes around. This dye has been successfully used on clothing for hundreds of years, so it's proven to stick around for a while. Always wear gloves, long pants and long-sleeved shirts when you are working with or near black walnut hulls.
Most black walnut trees are too tall for the average person to climb safely, so wait until the fall when the majority of the walnuts have fallen to the ground. Pick up the walnuts that have fallen, then wait a week to go after the remaining nuts that stayed in the tree.
Sort your black walnuts as you pick them up to avoid having to do it later. Inspect each nut as you put it in your bucket and discard those nuts with squirrel toothmarks, rotted portions or deformities; those of very small size should be discarded as well.
While there is nothing wrong with using your hands to pick up your black walnuts and willing children looking for extra pocket money can certainly be employed at this point, some inventive tools can make the job quite a bit simpler. For example, invest in a handled rolling nut picker tool. Instead of bending over to pick up the nuts, you roll the nut picker over the ground, much like a carpet sweeper on carpeting. The nut picker grabs everything over the size of an acorn from your lawn, depositing the items inside a basket or holder that you can then empty out.