Lately,I learned many new tricks in AoF(for every race(exclusive of dwarves and scaledfolks because I still didn't try them out)
So....
Humans:I am worst with this race(affected by the fact that I am bad in AoS too).But I can tell few things still:
Small maps:Swordsman,and two light cavs and pikeman too start with.Go with knights and heavy knights in mid game and late game(and make sure to have enough fortresses)
Medium Sized maps:Make defense,use cheap units to tackle the enemy at start,prepare for siege weapons,and heavy knights(make the game reach early-mid phase(almostly around 20 turns)).Then go with fireballs units and warmages.Imperials should be prior.
Large Sized maps:Just keep recruiting army and focus more on trebs and other seige and fireball weapons.Imperial knights in mid game can be big advantage too.
Elfs(which I got better all of a sudden):
This race mostly favours small maps(in my strategy,it does,but for the world,the are long map races)
Small maps:Since the enemy will probably have cheap units in start,make the two turn archers and wolf den,and elf druids to disturb his basic force.MAKE ATLEAST TWO SENTINELS,and some spearmen in early game(you need more TCs,which your archers will get.Don't allow enemy to spam.
Mid size maps:Basically the same,with elfs dragons in mid and late game,and ents.
Large Size maps:Take your time,plan everything,make sure you research many techs,elf can get many advantages this way.Try to quickly find out enemies location,and also,keep hitting him in start with 2 turn archers.
Orcs(which were my favourite,but I go little tired with their faces

):
Small Maps:Use swordsman and uruks,wolf raiders must be prior.Cannon fodders can be great.Don't use Green Dragons.A good player never uses something like that!
Mid size map:Do the same,but upgrade your army,and use giants in mid phase and late games.
Large size map:Focus on upgrading.Ologs,Ettins,Hamlets,Orc Leaders,Uruks,Trolls can make a havoc in these maps
Undeads(currently my favourite race):
Small Size maps:Go with knights and armoured and golden skeleton tech!Be sure to have armies to support you.Mummies and liches should be used in mid game.Use workers to build spirit towers regularly,make them as far as possible,and use necromancers and grave diggers to spam golems.
Mid size maps:Focus on the same strategy,assisted by death knights,spectral knights and vampires(skeleton dragons too)
Large Size maps:Go spamming golems and stronger troops like Death Knights