I guess play speed should be mentioned in any discussion. Also map size affects teching speed.
Marathon has unit training scaled at 2x, everything else at 3x. So, if you play marathon / huge then research timing is completely different from other choices. I play Epic / Large, and research timing for me is close enough to normal / standard that it can be worked out.
So, what do I build first? Depends
Workboat, if applicable. Up to two of them - even if I have more seafood I will need worker after two workboats.
Worker, if I have suitable techs. My primary purpose is to get my capitol to grow, so this generally means either deer + hunting or grain + agriculture. I do consider what the worker will do after first food improvement, and may need to either reshuffle my research plan or insert warrior(s) before worker.
Warrior(s) if neither of the above. I play without tribal huts, so I won't build a scout even if I have hunting. When I played with huts, I built scout often even if I had agri + grain or another combination suited for worker first, as the huts are random element that can grant you at least one difficulty level of gain in form of techs (which is why I no longer play with them).
My general plan is to:
- get capitol on growth
- get either AH or BW to see some strategic resources
- settle second city, preferably claiming strategic resource (sometimes I don't get AH or BW early enough due to unusual start where settler comes out earlier and other researach has higher priority).
I never, ever go for Meditation or Polytheism even if I start with Mysticism. Mysticism I consider simply wasted starting tech. Thus, Mysticism doesn't affect my early research / build choices.