People want to feel important. Making people feel important through honest and sincere compliments is the way to influence people.
Dale Carnagie says "The only way I can get you to do anything is by giving you what you want." p. 37
This doesn't mean you should flatter people. Flattery is insincere praise. But truly see what others accomplish, what they do well, and tell them.
When we are not engaged in thinking about some definite problem, we usually spend about 95 per cent of our time thinking about ourselves. Now, if we stop thinking about ourselves for awhile and begin to think of the other man's good points, we won't have to resort to flattery so cheap and false that it can be spotted almost before it is out of the mouth.
As Charles Schwab said, be "hearty in [your] approbation and lavish in [your] praise."