In our lives everyone has a circle of influence. The more people you know and interact with the larger that circle is. The same holds true in business I started off working on smaller properties, and a few well to do. It started out knowing a guy that worked for this lady that knew someone who needed a tree looked at. I know it sounds goofy but that's how it works. I network with landscapers, PHC companies, strictly lawn guys, rotary clubs and of course the fire department. The more people you talk to (assuming you aren't a complete ass, no offense) the more chances you have of getting on these properties.
The other thing is doing good work at a reasonable price. The well to do are no in their financial position because they are dumb with money. Some of my richest clients are the hardest on me when it comes to pricing. You can't just look at the car and say day rate + $$$. You still need to be on point when selling.
Good work sells itself. And I mean high quality arboriculture. They are normally looking for someone to educate them about what needs to be done and why. You do good work their friends see it when they come over the the wine tasting. And it's one question away from you working on their property too, "did you like xyz service?''. Also sweat the details, sawdust piles at a stump are generally not acceptable, any monkey can do that. Make it disappear, make it look good. They don't want to go behind you cleaning up and fixing divots.
(Not saying you aren't doing this all now, just putting what I have found out there).