In order to truly master Nami, you will want to learn her abilities and when to use them, and the builds needed to optimize her.

Abilities

Nami's Passive, Surging Tides, applies a Movement Speed increase to allies hit by Nami's W, E, and R. This can give your allies a swift boost to safety or help them catch up to an enemy champion to shut them down.

Nami's Q, Aqua Prison, throws out a bubble to the target location, dealing a small amount of damage and trapping anything inside for a short duration. When this ability hits an enemy, they become stunned as well as knocked up, which can be used to synergize with Yasuo's ultimate ability. Another thing to note is that this ability can trap multiple targets as long as they are in the bubble's vicinity, so you can easily stun multiple targets in a powerful set up for your team to engage on.

Nami's W, Ebb and Flow, shoots out a magical surge of water that jumps from up to two targets, healing allies and damaging enemies. If cast on yourself or an ally, it can jump onto a nearby enemy. Alternatively, you can cast W onto a nearby enemy, allowing it to jump to a nearby ally or another nearby enemy. Ideally, you will want to try and hit multiple enemies with this ability and utilize the jumping mechanic to your advantage. For example, if your ally requires a heal, but an enemy champion is chasing them in front of you, you can cast W onto the enemy, allowing it to then jump onto your ally to support them.

Nami's E, Tidecaller's Blessing, empowers an ally champion for a short duration, causing their basic attacks and spells to deal bonus magic damage as well as apply a slow to their target. You can also cast this ability on yourself, giving you a boost to your poking capabilities in lane with some empowered auto attacks. Keep in mind that this will also apply things like Aery, Ardent Censer, and even Imperial Mandate.

Nami's ultimate ability, Tidal Wave, summons a giant wave that will knock up, slow, and damage enemies in its path. Any allies in the wave's path will receive double the effect of her passive, Surging Tides, allowing you to set up for a powerful engage, or to tip the scales of a uncertain team fight.

When levelling up your abilities, you will want to prioritize W, then E and Q. Of course, you will want to level up her ultimate at level six and level eleven.

Runes

Picking runes for Nami is very easy, as she will only go one, maybe two different options. The primary runes here will be Sorcery, using Aery, Manaflow Band, Transcendence, and Scorch. Aery will help you do extra damage when auto attacking your enemy laners, as well as giving a boost to your supportive abilities by granting your allies a small shield. Manaflow Band will give you enough mana to sustain you throughout the course of the game, Transcendence will improve your ability cooldowns, and Scorch will apply a burn to the abilities you use on your enemies.

For the secondary runes you will choose Inspiration with Biscuit Delivery and Cosmic Insight, boosting your mana pool and granting spell and item haste, respectively. Alternatively, you can choose Resolve as your secondary runes and go with Bone Plating and Revitalize if you find yourself against a more aggressive botlane. To finalize your runes, you will want to select Adaptive Force for the first and second row, and Armor for the last; you can always replace the Armor with Magic Resistance if you are against two magic damage champions in the botlane.

For summoner spells you will of course want to choose Flash for one of your spells, and you can either choose Ignite or Exhaust for your second. Ignite is best against match ups that have another healing champion, like Soraka or Yuumi, while Exhaust can be really strong in almost any situation, as you can slow down and weaken an enemy champion.

Itemization

When playing a support champion you will of course want to start with a support item, and Nami will almost always go Spellthief's Edge. You can replace this with Relic Shield if you need a boost to survivability, especially against a hard match up. Now you will want to start building your Mythic item, which is going to be Imperial Mandate. This item is extremely strong on Nami, giving a huge boost to damage as it activates on Nami's Q, E, and R. Your next item can either be Ardent Censer or Staff of Flowing Water, then you can build Redemption. You can build Mikael's Blessing as a second or third item, alternatively, if you need to rescue your allies from specific crowd control abilities like Malzahar's ultimate or Veigar's cage.

For boots you will want to build Ionian Boots of Lucidity, as the Ability Haste will be the most useful trait for Nami from our options. Be sure to always grab a Control Ward when available, and to replace your trinket with Oracle Lens when you have upgraded your support item.

Laning Phase

Nami has a very strong lane presence between her heals, stuns, and poke. You will want to trade with your enemy using your E and throwing out auto attacks. You can also use W to poke, especially if you need to also heal yourself or an ally, as you can get the ability to jump and serve both purposes. You do not want to poke using Q, instead, save it for when you see a good opportunity to engage and shut down your enemy so you do not waste mana or force an engage when you are not ready. If you and your carry get engaged on instead, you will want to use Q on the enemy carry so they cannot shut down your ally, and be sure to keep them healed with W and empowered with E. You can use your ultimate to engage or disengage, but it is best used at close to medium range, so that your enemies can not move to safety before the wave hits them. Be sure to keep wards up in the river and to look out for the enemy jungler, since you can easily stop their advance with a quick Q. Roaming to help your jungler or even your midlaner can be easily done whenever an opportunity presents itself, like if your enemy laners have just returned to base or have been defeated.

Teamfights

You will obviously want to heal your allies when they are in danger, but you also want to empower them with E to increase their damage, especially if you have Ardent Censer and Imperial Mandate built. Empowering your carry is going to be the best option here, so that they are continously shutting down enemy champions. However, if your carry is not currently at the fight, use your E on other key damage dealers in your team. Save your Qs for key targets, like the enemy carry or the enemy jungler during a fight over an objective. You do not want to waste Q on an enemy who has not built many items and is not a huge threat to your team. You can use her ultimate to either set up the initial engage for the fight, or save it to be used when all the enemies are grouped up, so your team can follow up with their own ultimates to create an entire field of damage and crowd control.

You will want to position yourself in a spot where you are not close to the enemy team where they can engage on you, but you want to stay close to your allies so that you can keep your abilities on them at all times. Nami can be easily shut down if focused, and the enemy team will happily take down the healer who is keeping the team alive and safe. You want to be able to trap an enemy in Q if someone gets grabbed by a Thresh or a Blitzcrank, so they cannot easily burst down your allies. Using her ultimate when someone gets stunned on your team is another way to buy your team time in a dangerous situation.

Conclusion

Nami is a strong support pick with healing and empowering abilities, as well as crowd controlling abilities. She can support her allies by granting speed and health boosts, while also being able to trap enemy targets and help shut them down. While not the tankiest, Nami can be easily focused and defeated, so she should not be used in close distance to fed and powerful enemy champions. However, her speed and crowd control give her a lot of options for an easy escape. Mastering Nami can be fun and easy, as long as you remember her strengths and weaknesses and the role that she plays in her team.