Nothing is more important than the inital rush. So grabbing all the yellows you can is the top priority. My method calls for saving the PQ 14 and even PQ 13 planets for the second wave that comes later by basically picking one planet to be your colony ship builder. Keep autolaunch off for that planet. When the ship is ready, pick your target, plop down 100-200 million folks (depending on your morale bonus and whether it is a PQ 14 or PQ 13), and send them on their way. A few turns later, when the next ship is ready, repeat. This way you slowly add to your empire.
To keep costs down, build nothing that costs more money than it is worth on the low quality recruits early on. In the early game, this basically means buiding soil enrichment, habitats and a bank. A little later in the game, when the economy is better, I add entertainment centers, research labs, and manufacturing centers. The next stage after that slowly adds anti-matter power plants, stock exchanges, teleporters, stadiums, economic exchanges, and terraforming.
That is a bare bones model. Of course, if a system has specialized needs, add that to the list as well. It is quite common for me to add a news network to prevent a culture bomb if it is a colony on the border of another empire (or, better yet, inside another empire). If I get lucky and one of these lower quality systems has a high influence, then I might add an embassy to help start a culture bomb of my own. And a system that looks like it might be the frontline of the next human-alien war might get defenses, for example.
In the end, these planets turn into PQ 15 or better. They usually don't end up being star players, but they do their part helping my economy and giving me influence.