Early game
Your goal early game is to mulligan sites and hopefully get a defensive site in your second forward spot, slowing your opponent down until you can get 5-6 mana, and 3 air threshold. Bottomless pits are top teir, with void, perilous bridge and great wall also being great options. Play the rest of your sites in the back row, being mindful of you threshold being cutoff from atlantean fate. If you get witherwing heights make sure to have them nearby to Bottomless pit and Void to toss unwanted attackers.
Mid game
Your gonna hope for an early poison dagger, so you can remove any 1 enemy for 3 mana with your avatar. When this happens, all the pressure will be on your opponent and the game will feel easy. You want equip most relics onto your avatar, unless you have a move you can do alot of damage in 1 turn, or door your opponent. This part of the game is a balancing act where your trying to keep the board clean hopefully with your creatures but using avatar as necessary. The healthier you stay in this part of the game the better, using vampires and grappleshot and whirling blades to clear board and heal.
End game
At this point you will be playing mostly 1 card a turn, trying to hold a grappleshot,toolbox, tactical move while positioning for the deathblow. This is of coarse if you didn't equip a dagger and ring of morrigan and watch your opponent flip the table when they feel the full power of Adtonitum.
Things to watch out for
Avatar of air doesn't care for your sites placement as they play similar and can use your defensive sites against you.
If your playing against a water deck, and instead of building sites around your defensive sites, they start placing minions in the back row, your about to get ruler of thul/polor explorered. Place sites and minions accordingly to counter there attack.
Fire decks HATE to see bower hit the field. Boudicca/morgana/courtesian thias/saracen raiders all turned into puny beasts. The only mortal your running is princess which is worth nerfing to shut opponents heavy hitters off. Most of the time you can mulligan bower but if you know your against fire, hold onto it.