I agree with Hearteater. When I start out I find the AI planets closest to my Homeworld that have the most metal spots in order to boost my economy. Then, playing with Core Shield Generators enabled, I go for the most beneficial planets with each Core Shield (B, C, D, and E), whose value depends on distance from my Homeworld, how many metal spots they have, and of course what super weapons, fabs, or turrets they have on them. For Core Shield As, you have to kill 4 of those regardless, and those all come with a bonus ship attached. Of course destroying those is a lot less convenient because you don't really get to choose the location. After all the CSGs are down, you should be ready for your first attack on the AI HW!