I hate to tell you this, but there is no easy way. I spent YEARS searching for that perfect lip color. I think I've finally found it, and yet everytime I am in the drugstore I find myself looking at all the lipsticks and glosses. I just can't help myself. Not that a person has to be limited to just one color. I may wear a different color everyday depending on my mood.
Back to the topic at hand...for an everyday color that will always look great, look at your natural lip color. Your best color will be a shade darker or brighter but not far off your natural color. When you wear it (even with no other makeup) it will make your whole face look brighter.
For most people this is going to be a pink, pinky brown or pinky peach shade. Sometimes you have to leave your comfort zone to find the right shade. I was always looking at pinky brown, mauvy colors and noticing that I had about 20 variations of the same color at home. One day I decided to try Maybelline's new Shine Seduction liquid lipcolor. Instead of buying my regular pinky brown I picked up "Champagne Fizz" - a sort of peachy color. Well let me tell you - I LOOOVE this color. It looks pretty and natural and so far I haven't tried it on anyone that it doesn't look good on!
I think the Shine Seduction line is a great place to start looking for a lip color because the colors are very pretty and sheer, and even if you want to try something new like a cherry red, it's not going to be over the top dramatic.