After the debacle in the previous scenario, you will no doubt appreciate an easy one. All the portents bode well here. Despite what the scenario instructions say, you have plenty of resources. With little more than your initial force, you can get a quick kill.
There is far more food and wood available than you can possibly use. There isn't much stone immediately available, but you are only going to build a few walls. There's not much point in building Towers, what with all the heavy artillery running around. Assuming that you get Coinage right away, your initial base will provide you with almost 1,375 gold. That's not very much, but it allows you to get 4 priests (500), 4 Cavalry (320), 2 new fast Phalanxes (100+80+150), leaving 225. You will need more eventually, but the scenario will be pretty much over by then.
Explore your landmass. You have available two catapults, a Scout, and Caesar, all good scouts. Build a Town Center right beside the forage bush. Also build three Houses, and then produce four more villagers. Collect only food and wood to start, and then, as you work up to 15 villagers, get some stone and gold as well. Get Coinage early. All of this is straightforward.
There are only two approaches to your base: a wide ford and a narrow ford. Everything else is impassible. Wall off both fords entirely. There are two alligators in the wide ford. You could kill them and eat them, but this will require a significant amount of micromanagement, and there is far more food on the map than you could ever use, and time is far more important here than a little bit of extra food.
Not far from the narrow ford is an area with a lot of all types of resources. It is guarded by a lot of lions, including some bosses. You could easily kill these lions and get the resources, but then Red will get mad at you, so let Red fight the lions. The AI does not do this effectively, so Red might lose a fair number of units over there.
Build a dock beside the wide ford and produce a fleet. Six War Galleys are enough to guard both fords. Make sure that you don't accidentally attack Red. Explore the river system as far as you safely can.
You will note from the Achievements menu that Yellow is actually very weak, while Red is very strong. You could certainly win this scenario by killing all your enemies, but both of them have vast amounts of resources and will eventually get exactly the same types of units as you. If you spend any time at all attacking Red, which is completely unnecessary, not only do you give Yellow time to build up, but you also will get Red very mad at you. Therefore we are going to avoid Red as much as possible, exactly as we have been told to do.
Produce a large Transport. Load up your Scout, Caesar, both catapults, and both Hoplites, and invade Yellow territory. You could do this very early, but there isn't any point until you have set up your infrastructure, because you simply can't control it all at the same time. Take along a couple of Triremes for naval support.
You are immediately in contact with some Yellow Towers. You already outrange them, but get the two main catapult upgrades anyway. Blow away all the Towers you can. Be prepared to withdraw into your Transport, while your warships and melee units deal with the enemy response. You will need to bring over some priests for healing. You will also need the two main upgrades for Academy units. It is very important to kill every repairman that Yellow sends into the area.
Fight your way inland, bearing to the right. You are killing so many troops and villagers that Yellow will already be broken, and it's just a matter of mopping up. Your only real concern is that Red might come over and hit you in the flank. Bring over a second Transport group of 4 Cavalry, two more Phalanxes, and some villagers. Build a wall from the Yellow position to the river to block off your left flank. Leave the slow units and warships there to defend the wall, and advance your fast units and Catapults into the Yellow position along the map edge, and then around in a counter-clockwise direction, blowing up everything in sight. Start sucking in some of the massive amounts of resources that you find there, especially the gold.
By the time Red decides to attack you, it's probably far too late for them to be able to prevent you from quickly blowing away the last few Yellow buildings.