Ater you have chosen your castle, upgrade the City Hall to level 3. Then, buy 2 extra training slots and an extra build team. Upgrade your armoury and Tower of Trials to level 3. Buy a Bronze Shortsword and Equip it on your starter hero (preferrably Rickon or Meera, but Grismund is fine).
Then, Upgrade the shortsword to +3 and go to the campaign screen. Attack enemies until your cd turns red. then, if you have gold, speed up the cd, if not, go and have a snack. when you get back, or when you use gold, attack the Elite Vanguard I, that gives a scale mail. if the cd has finshed, upgrade the scale mail to +3, if not, use gold to speed it up. Level your City Hall to level 5, do the same for all your other buildings.
Equip the scale mail on your hero. Fight battles until you defeat Maid Marian, recruit her as one of your heroes and put her in training straight away. If you can, add exp to her 3 times. you should have done this with your starter hero already, buy a rapier and get another scale mail from the army. upgrade both to +3. Now Complete Sherwood Forest and do SFL once. if you recieve a Shire Horse, upgrade it to +5 and do the same with all your other gears.
Move to Center City
Upgrade to level 8, get all other buildings to level 8
Now, Do what you like until you have defeated Baldwin, Join King Arthur and if you are one fo the first people, set up and alliance, if you are later, join a stronger one.
by now you should be around level 12-15, max all your gears and max your academy and research. upgrade the gold lance to +12 and repeat, making an identical gold lance +12. go as far as you can in Viking Invasion, then start farming prestige until you have 20000. recruit Sir Kay and put him in training.