Place your stockpile near grass and stone patches. Build a granary quickly, but you can actually delay food production for the first ~10 minutes if you focus on popularity elsewhere.
Before jumping into Skirmish mode, it is highly recommended to complete the in-game tutorials. Firefly Studios Support notes that the game includes a small tutorial campaign and three learning campaigns designed to familiarise players with different factions and mechanics.
Money is essential for hiring mercenaries and buying missing resources.
Build your archers on walls or towers. The higher they are, the greater their range and cover.