The main objective that must be done early on is to get your Castle
to the highest as possible level. It is best to upgrade to a level 10
Castle ASAP then catching up with the building upgrades later. Only
level up the buildings that are required for castle upgrade.
Level up the most important buildings first
Once your castle has reached level 8-10, you can begin to catch up
with leveling all the other buildings. Work on increasing your nation's
population and ensure that all resource buildings are upgraded first,
along with storages. You would get more resources from the world map
later, but early on, the resource buildings are the most important. All
other buildings except for those mentioned are not important, just catch
up with them after Castle level 10.