think about the paint scheme of your plane irl. Is it shiny and new like a B-24 fresh off the assembly floor? Is it dark and stealthy, shrouded in a dull black? Is it old and worn, dawning a faint olive drab? Do you want it to reflect, or do you want something more subtle? How modern is it? Just a few questions to ask yourself.

Also, thanks to my friend, Xogo, we've developed various winglet systems for super-sonic flight and trim. I can tell you how to make one of ya'll so wish~

Use gloss, people like shiny colors, it looks clean and new.
Make your plane streamlined, it looks very good if you do that
Make cockpits to cover the default one with fuselage blocks and fuselage cones.

So you can color the bottom and top a different color @Viper28

Use a double wing

Put jet engines in nacelles. They look better that way.

Make sure you smooth out the corners,

NEVER USE THE DEFAULT PAINTSCHEME

in a final release (or a prototype, really) unless you want to be likely brushed over. I've seen this happen to golds too, they use default paint and most think its a noob-plane until they see the username.