Agree about looking at the map.
Occasionally, I have a goal / victory in mind before I start the game. "Supremacy with XX leader" so I choose the planet, biome, and load out to match the goal.
Most of the time, I pick a leader and play the map. I first look to see if I have enough land to build my empire and leave space for earthling settlements, which must have the same minimum spacing as cities. If not, then Purity becomes secondary. I have a soft spot for Harmony, as it helps me grow out of the Health deficit, but that may be more *my* personality rather than the leader I'm playing. It's a victory condition for a "builder", which is what I do more often than warmonger. I don't usually try for a quick Domination victory.
Most of my games I have plenty of access to the strategic resources (Floatstone, Firaxite, Xenomass) so that I'm not constrained for building advanced units. Once I've chosen a VC, I figure out where to put the victory wonder so that I can defend it easily.