Gather resources when away
If you are not going to access the game for a long period of time, it is best to leave your army out to gather resources in the world. Cavalry could carry the highest amount of resources while archer could carry the lowest.
What to research?
It is best to research constantly following the game's recommended route early on, for rapid production. About the troop researches, focus on the Troop Promotion to be able to upgrade your trash units into better ones. Always look at the instant benefits that you would get from researches and focus on those more pragmatic options, as the higher tiers are really expensive.