NamiShe have one of the best lvl 2 all in if your adc is aggresive,your Ebb and Flow can bounce 2 times,wich means that you will hit 3 targets,and your Aqua Prison can stun a enemy and get a kill
But be careful if your adc is not aggresive don´t lvl up your Aqua Prison,instdead of it,lvl up your Tidecaller's Blessing

NamiWaste a lot of mp at early games,just try to apply the Manaflow Band as soon as possible.
When you reach lvl 6 and lvl up your Tidal Wave if they have a aggresive botlane,save it to disengage the enmies but if they are squishy,use it to get kills

Nami´s Tidal Wave is core at the teamfights,it is a hard cc ability in a big area just land a good Tidal Wave and you will win the teamfight if your team follows you.
Try to boost the adc(or the feed of the team) with your Tidecaller's Blessing and knock up the enemies with your Aqua Prison
Nami is not a strong healer as Soraka so try to heal your team when you have extra healing of the Athene's Unholy Grail

Build Rabadon's Deathcap if you want more dmg but if your team needs mobility build Shurelya's Battlesong

Yes,if you have a premade as adc Nami can be a beast of the game doing the teamfights almost impossible to win to the enemy team by using your Tidal Wave
But remember Nami is squishy,that means that she can get delted by a lot of champions just be careful with your positioning

I will start to upload videos to youtube and do guides of supports.
I´m a support main since 2015,when I started to play league of legends.
I hope I can help you,I will do a guide of each support and upgrade this guide as soon as I can.
Sorry for my English Level ^^
My youtube Channel:https://www.youtube.com/channel/UCrdHAoN0VkTq0UwXT3W2jRg