Namis AP falls off hard late game so its a good idea to have utility runes and masteries, Nami runs out of mana very quickly due to her heal costing so much, mana regen runes help a great deal when it comes to this. Try to stay with your ADC all game and this build will serve its full potential.

This build Is mostly a defensive build, Ardent gives some AP so that your heals will heal for more, but for the most part you shouldn't need much AP.

With this build you are not going to have very much damage, however you will have great utility and be able to stay in lane with your ADC much longer than usual.

If you are against anyone with a pull, it is going to be difficult to survive unless you can hit your bubble on both the ADC and Support.

This build has a lot of item use, you are going to need to be quick when using them, and try to space it out during fights so the enemy will never know if you can shield or heal for another 300 hp.

As support You should almost always be with your ADC, follow them around and make sure that they are never alone. If you are ahead in lane and feel like your ADC can handle themselves without being killed, roaming mid lane to pick up a kill is a good idea.

I personally Like to take exhaust instead of Ignite because your goal on this build is to keep your ADC alive the entire game. While ignite can offer damage early game, it will not do any good if the enemy team has an assassin.