After being in this field for over 30+ years I have acquired some pet peeves or do-not's. The list isn't real long but could save your plants, some money and a few headaches. We'll start with trees.
Biggest tip is to hire ISA certified professionals, get proof of insurance and don't let them us boot spikes on the tree unless is is coming down.
We have workshops twice a year in Mount Dora to help share important tree care tips for homeowners and professionals as well.