There are several ways to level a hero

 

The most effective one is using them on your attacks ( dont risk them on suicide attacks though unless they are valuable ) and larger the battle is the bigger experience your hero gets. always upgrade your heroes so you can profit more from their attributes. watch out for heroes that have high attributes of all or 2 stats because they become very useful when you redistribute their stats using holy water ( higher lvl costs more ).

Another way is appointing your hero as mayor and just do your own business. they get experience from buildings, troops you recruit from barracks, researches, wall fortifications but they get experience when timer is done, not when you start those. they also get experience when someone attacks your city because your mayor will lead your army while defending your city ( so you better keep your attack hero as mayor while you think someone big is going to attack you and you think you can handle it).

Few = 1 – 24

Pack = 25 – 49

Lots = 50 – 99

Horde = 100 – 249

Throng = 250 – 499

Swarm = 500 – 999

Zounds = 1,000 – 2,499

Legion = 2,500 – 4,999

Bulk = 5,000 – 10,000

Giga = 10,000 – “Infinite

Walls - suggested defence - personal preference varies 

2000 traps

2000 abatis

the rest in Archer Towers

Do not build rolling logs and falling rocks.  They are expensive and take a lot of space.  They are easily taken out by warriors.

Build wall defences in small amounts at a time - the sooner they will be ready and able to defend you city.

6-7 cottages

14 + barracks

Warehouse is optional but no more than 1

1 of everything else

Inn - only upgrade to 1-2 - no more

Embassy - minimum level 5 as soon as possible - make sure it is checked to garrison troops

Beacon Tower to 9 as soon as possible

Stable, forge and workshop only need to be upgraded to 10 in one city for research.  Other cities only minimal levels to build walls and relief station. After can be demolished.