Woodcutting 1: Before training
Farming 1: Before training, except if you have a lot of additional food
If you have a slinger civ and collect stone early, you can also take the stone upgrade early
If you have like 100 pop you can go p2 and then immediately woodcutting 2, then farming 2.
After clicking p3 you can also take stone 1 and metal 1.
After reaching p3 obviously take wood 3 and food 3.
stone 2 isnt really worth it, unless you plan a lot of slingers during a long game.
Metal 2 and 3 can make sense if you have extra metal.