A method I often turn to is fashion fabric, the clothes in my closet or the clothes I see other people wearing.
When I'm in the store and not sure if the 'green' I'm looking at will play nicely with the 'yellow' I'm in love with --- I browse the fashion fabric and can usually find the 'yellow' in a print that includes other colors --- I may base the 'green' I buy on the shade that is in the fashion fabric. Does that make sense?
I also look at the clothes I own and the colors other people choose to wear. That is how I figured out that lime green and navy blue look awesome together. And that red and black is a severe look, but red and dark brown is a softer look.
My husband thinks I'm a rude people watcher, but I'm not being nosey, I don't care what they are doing, I'm checking out the patterns and color combinations in their clothing!