Lately, I've been experimenting in the opposite direction from most of the posts above.
Turn 1: Turn off military spending; buy 1 factory and start building another; buy a Deep Space Scout (cargo hull crammed with engines and sensors); park the starting colony ship in homeworld orbit, unless the survey ship spots something juicy right away.
Turn 2: Return spending to an even split between the three categories; get to three factories before building other structures; start building a colony ship.
After: Keep building colony ships - pretty soon they'll pop out every 6 or so turns. Don't rush buy them unless you need to. The natural pace of shipbuilding with three factories will allow your population to keep growing and increasing production. I never move homeworld spending focus to any of the categories unless I'm desperate to crank something out ahead of another culture.
New colonies: purchase the first factory, set spending focus to social, let the colony build two more factories on its own, go from there.
All of this puts me way behind on research during the initial colony rush, but I accept that because, with all of those factories going online early, I can build things pretty quickly on each planet. Plus, I can usually at least keep up with the others' research through tech trade until I get my economy fired up.
This comes in very handy when upgrading all of your planets to research academies, for instance. I very rarely have to purchase my spaceships or structures in the mid-late game, and can save my $$ for things like massive (several bases each turn) influence starbase upgrades. I just won my first Metaverse game after starting out this way; an influence victory over six other races in a huge galaxy.