You'll want to:
Have valid fishing permits if required.
Check the laws to see what fish you are and aren't allowed to bring home for your aquarium, any size limits, etc.. (Invasive fish species are usually illegal to transport or possess alive no matter where you found them. Non native fish aren't always classified as invasive. Some states have regulations on keeping some legally caught natives in aquariums too)
Be able to identify the fish you do decide to take.
Check the laws regarding what methods of capture you are allowed to use on which species (sein, dip net, cast net, hook and line, etc.)
Never release fish back into the wild, even natives.
If transporting fish in buckets you'll have infinitely better luck if you have a battery powered bubble box to aerate the water.
You can keep natives with other fish as long as their temperments are compatable. You'l want to quarantine any wildcaught fish before mixing them with fish you already have, but this is common sense.