This has been my greatest secret weapon in business and it takes very little effort.
The amazing thing about being nice to people is that usually, no matter what, they feel like they have to be nice back. Or, at least cordial. What to do if it's not easy for you to be nice? Well, then fake it for crap's sake.
What happens when people enjoy being around you? They prefer to do business with you. I prefer doing business with people that are nice to me. I mean, that's just basic. Now, this is all not to say, hey, let's make everything free and easy baby. Ya know, eventually, momma's gotta get paid.
But it's way easier to give my money to a nice person than it is to give it to a d-bag.