Athena support

For the starter build :
Athena has a strong early game, u would like to rotate around the map and stay as much as u could in the battlefield. While in the battlefield, watcher's gift will allow u to achieve gold much faster and even have the most gold in your team in the early matches in lane.
You would like to rotate, invade and taunt as many people as you could you need to grab shoes, and 4 hp and mana potions.

build :
level 1 : upgrade ur 3rd ability - with that go after the enemy's archers in lane ( full clear at level 1 with ur adc ability).
level 2 : taunt (2nd ability) - if u cleaned the wave as said above, you'll have lane control and you'll want to invade purple buff/red buff. as u getting taunt u are basically securing the invade and getting free damage on the enemy.
level 3: dash (1st ability) - it will allow u to rotate to mid lane faster and secure mid harpies and gf harpies.
level 4: 3rd ability - faster wave clear and objective clear.
level 5: your ult/your 3 - your ult will allow you to rotate much quickly and help other lanes, but ur 3 will help you to secure lane control and invade more buffs in your dou lane ( purple and red).

As your shoes, you will like to grab the reinforced shoes. It will make u much tankier and help you both in lane and in team fights.
If you are against a physical adc you really want to grab sovereignty first.
If you are against a magical adc you really want to grab heartward//pestilence(if they have healer) first.
Winged blade is an important item in your build. It will allow you to rotate much quicker and make you much healthier.
Spirit robe is the most important item in your build, in a team fight most of the time you'll want to be in the frontline. With spirit robe you'll get cc reduction and more defenses and survive abilities.

If your enemies' main damage dealers are physical you'll have to choose between :
Valor, Shogun's Kusari, Discord.
Valor- will grant u some more CDR, you will have the ability to go in and out with your ultimate in a fight so your team will get a massive advantage! (6v5 kinda).
Shogun's - If your team has 2 adc's ( hunter or magical hunter) you could pick that up and make them attack quicker, it's a solid pick tho i won't recommend it always.
Discord - more overall protections, and even a stun during 30% health, with the cdr will help u get in and out during a fight.
If your enemies' main damage dealers are magical, you'll have to choose between :
Pestilence - overall a great item. mostly picked because of it's passive(anti-heal) but 80 magical protection is great.
Genji's Guard- A great pick up by athena, 10%CDR will help you to get your ult faster, rotate around the map and even go back to base and ult back during a fight. It has 70 magical protection a little less from pest, but overall a better pick up.
Discord - more overall protections, and even a stun during 30% health, with the cdr will help u get in and out during a fight.
If your team are mostly using magical damage, you can consider picking up Void Stone, it'll help them do more damage and give you some magical defense as well. It's a nice pick up but I really don't like it personally.