What are some recommendations you’ll give a new ads-b operator
This is very generic advice.
Whatever aerial you get, for optimal performance, mount it as high as possible with as clear a view to the horizon as you can manage. Feed it with good quality coax and keep the run as short as possible.
Completely agree. Last June I moved my FA 26" antenna from hanging inside a window on the 2nd floor of my house, to mounted at the peak of the roof, with the base exactly at roof level. Overall, it is probably 12 feet higher than it was. I changed from 3 feet of generic coax to 50 feet of higher quality stuff, but other than that, the same Pi, receiver, filter, and antenna.
This is the difference in message rate and aircraft count:
Some things to consider.
Do you want to build or buy?
Will it be mounted inside or outside?
Do you have a budget in mind? (most people start very cheap and work up)
Otherwise, what @keithma said.