On day 1 you need to build as much houses as you can to grow in population. This is the perfect build guide for the first few days in Diplomacy is Not an Option:

On day 1

1. Build 3 lumbermill in a row near the best forest area to your main castle. Don't split the lumber mill into different location on start up. Just build them in a row to get as much wood as you can.
2. Build 1 fishermen's hut
3. Start to build as much houses as you can till the next day begin. You can rise your population grow for day 1 to 19-25 people for the next day
4. Hint: Take your soldiers and look arround for wook carts. Collect the wood and build more houses on the first day.
5. Hint: Take care on your build positions and let the builders have short ranges and nice paths to the next construction site. This speeds up the construction.

On day 2

1. Build 2x Builders Houses
2. Build 1-3 more lumbermills without storage in a good position
3. Build 1-2 stone mines
4. Spend the rest of your villagers for berry pickers
5. Keep walking arround with your soldiers and try to kill as much enemies as you could

On day 3

1. Build barracks
2. Build one more fishermen's hut
3. Build some more houses (you need 9 villagers left on day
4. Build 1-2 more stone mines

On day 4 - first wave incoming

1. Wait until you know where the first wave is coming from. Build a single wood tower directly in the path between the horde spawning point and your castle
2. Recruite 9 more archers and put them into the tower.
3. Place your 4 other knights, 4 archers and your catapult behind the tower

On day 5

1. If you done your job well in the past 4 days you should be able to upgrade your castle right now.