If you take out the trash items you dig; you won't have to re-dig them the next time you're at a particular location.
Do your very best to leave NO sign that you were ever there
Practice in your own yard to develop your techniques for digging, probing, recovering that leave no sign; or at least no sign that can be seen without walking right up to the spot; one that will disappear with the next rain. Take great pride in leaving no sign. THAT will give you the best reputation.
If there has been no rain for awhile, do not dig. Use a screwdriver to recover targets no deeper that grassroot level. You will find that most of the good stuff will be no deeper than root level UNLESS the area has been filled in and / or re-sodded in the past. If the soil is moist enough to use the plugging method, use the method that greenskeepers at golf courses us to relocate the cups. Clean, DEEP plug that keeps the grassroots secure in the soil. Again, practice in your own yard and get your methods down pat before carring it out into the parks and other private yards.
Get permission from property owners BEFORE hunting their property. If the owner of a vacant lot lives out of town, get their permission first. Don't say, " well nobody will care. It's vacant land." If you don't have permission, STAY OFF OF THE PROPERTY. (Capitalizing those words are not yelling........it's for EMPHASIS) One of the ways we hobbyists get the bad reps is by people ignoring common courtesies and not using common sense.
When you're hunting a park, yard, or school area; try the hard places, too. Look under the big, old bushes. Look in that narrow strip between the old bushes and the fenceline.