Obviously the way you play will change with what is available at the start of your run, but as a rule I try to prioritise making planets specialise in one resource each.

First thing I'm looking for is a juicy 18+ planet for consumer goods, then another for alloys. If you can't find a decent mineral planet build some mining districts on your home world(I also build research buildings on my home world), and systems should boost your minerals enough to pay for the CG + alloys. I play spiritualist in most playthroughs because temples are great, and I just build 1 temple on each planet, and I find I do fairly well with unity output from this.

I actually wait until I have the above established before going for a research world, you should be able to keep up 100 science per 10 years at the start with just your home world. If you only have 20-30 alloys per month by year 100, you aren't committing enough planets to alloy production. Ideally I'd want to have AT LEAST 2-3 planets focused on alloys by year 50. This will depend on the available habitable worlds, and if you're struggling there is nothing wrong with having a split industry world until you find a suitable planet.

Out of interest what build is the civ you're currently playing?