Food
You can often tell where enemy settlers are gathering their food from by looking at the hunts near their town. If you see dead animals there, chances are there are setters there. When you send cavalry (or any other unit) there to raid, always try to strike from the direction of their town. Your opponent will be hesitant to send his vills back to his town seeing as your units are blocking the way and creating pathing issues. You're bound to achieve more casualties this way.
Wood
You can tell a lot of the time where your opponent is gathering wood from by scouting the trees in his area. If you see falling trees, that's right - there are enemy vills gathering wood there. This is not as easy as hunt-spotting because each tree holds 300 wood and gathers slower than food so you need to observe closely.
Coin
This is, in my experience, the trickiest resource to catch your opponent out at. During early to mid-game, if you click on one of your vills and hover the mouse over a mine, you can see whether it is depleted or not. If a little pickaxe icon appears, that means the mine still has coin left in it, if there is no pickaxe icon there, that means one of two things.
1. He has found another mine and is currently gathering from that one.
OR
2. He has built plantations
General Tips
When you raid, something subconscious will happen - your opponent will "fear the fog". When you raid a lot, he will expect attacks left right and centre. This can even mean he results to building plantations and mills to sustain his economy, granting you access to the most valuable resource, and I don't just mean hunts and mines. The most valuable resource you will gain access to is Map Control. If you deny them food, you deny them the game.
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