1. Learn important shortcuts. It does make a difference, saves a lot of time, some common ones.
g - Granary
m - storehouse
t - Temple
b - Barracks
a - Archery range
r - Armory
x - Market
, - idle villager
. - idle soldier
As you play, look at the things you are using regularly, all the different buildings and make note of their short cuts. The more you use the keyboard, the faster and better you are. All pros play mostly with their keyboards, less with their mouse.
2. Always watch out for population size and idle villagers. The less you are idle and the less time u waste waiting for pop, the faster and harder you can attack.
3. In the beginning, produce an army according to your resources. For example, you had a lot of food but not so much gold, going for hippokins here is a bad idea because eventually your production will stop. Doesnt matter if poseidon gives them a boost. Also, if you still insist on making hippos, move your villagers about, take some from food and put them to gold, get gold upgrades.
4. Every single soldier is prescious. At one point i saw a hippok. run into his base and just die without doing much. This again is a waste of time and resources.
5. I saw you attacking buildings with archers. No point in doing this, when you have archers and hippos like that, let the hippos attack the buildings and the archers pick out the enemy infantry. You take less damage like this and can attack for longer. Also, go for villagers first.
6. Took too long to take the settlement. Should have done it immediately after he used ceasefire
7. Train myth units, they are there for a reason. Obviously dont overdo it, but you had a lot of wood not being used for anything and you could have made centuars with those. 3-4 is enough to do painful damage to his economy with a hit and run strategy...
8. Villagers before buildings. There was about 10 or so villagers mining gold in ur face when u were attacking buildings even if you just kill 2 and make the rest run away, that stops his supply of an army. This way you will eventually have the advantage.
9. Work on your micro. You lost a lot of units for no reason, when you were trying to take out his buildings. Going after buildings in the beginning is pointless, he can rebuild because his economy is still alive. This is why he caught up to you.
Edit:
Here is the example game i promised. Its not GREAT because i havent had much practice with Poseidon but the basic theory is there. I prefer loki and kronos to any other.
http://www.pclive-assistance.fr/share/files/get/JF-eyNXxzp/poseidon-eg.rcx