So we all know that more colonies means more cash and hunting opportunities in the long run, but now that you have researched that astro, where should you go?
Personally I always put my first two colonies in the same system as my HP. Not all players do this, and I don't even know if it is a good idea, but lets not focus on that. Once your ready to get out of your system, then what? Well, lanx is the key.
Lvl 5 gets you 24 systems and lvl 6 gets you 35 systems that are scannable. Now, to avoid overlap, your systems should be twice this number apart (whichever one you will go for, I recommend lvl 6). Realize that eventually you will have moons on all your planets and so this can be a work in progress.
If you move into another galaxy, you should try to go right in the middle of the galaxy (unless you are hunting a specific target... more on mobiles later). This allows for expansion in either direction rapidly.