the first thing i do (turn one ) is set empire wide production to 100% and then never touch that slider again.
after that when i colonize a planet i put down 2 factory's. (i determine their placement on if this is going to be a manufacturing/ or specialized planet)
then i do assembly projects and leave the planet to auto-upgrade
when i get an idle planet warning i check over the planet and choose buildigns base on what the planet should be specialized in and let it auto upgrade
when i get an idle planet warning i check over what i've built and adjust the planetary spending appropriately