it depends what you want to do with it.

if you just want a secure base for mines and res generation go far out to some remote galaxy (7 or 8). If you wan't to use it as another base for raiding from, stay in the populated galaxies, like 1 or 2 and just locate it a couple 100 sytems away from you. If you just wan't to ship all the res back to your homeplanet then just locate it in your system, however this will mean that if someone wan't to attack you, they'll now have no problem finding your second base.

also to take into account are the average field sizes. you basically want a colony that has 200+ fields. anything less than that you will find that as you progres in the game that you will find that you simply can't build any more byuildings for lack of space, which is a bad way to be. Rember every level takes up a field. the position in the sytem also has an affect on the field size.



so for larger fields go for position 4 - 6. remember that the closer a planet is to the sun, the more efficient your solar sats are, but the less efficient deut mining is. so 13-15 give the most deut. 1 - 3 are good for solar sats.

basically colonising depends on your style of play. if you wan't to turtle it, you know use it for res, get it as far away out of the populated systems as possible. if you want to raid lots, stick it in the middle of galaxy one or two. it's really up to how you think you will play the game.