The first thing to do is to get yerself a nice map from the PagesOfNowAndForever, so at least you know the location of the alien race´s spheres of influence. Now the very best minerals are the Exotics, which are purple, then the Radioactives, which are Orange, NOT red, and then the Precious, which are golden yellow. And the 1=1 minerals , the commons, are actually light blue when found on a planet. If found En Masse, the Grey globs,1=2, the Base Metals, are actually worth something, htough less so in the later stages of the game, since if you get your flagship to a real killing machine, you get all the RU you need from combat. Go kill VUX with a Spathi. It´s easy money. Also, you should visit Zeta Sextantis I, in VUX territory, it´s the closest Rainbow World at the beginning. How does 500 Melnorme Credits sound?