Alright, this is just my style of playing Nami, but it may not be for everybody. I play this particular support to for the purpose of feeding my adc early, warding constantly and changing team fights. If you chose to play this style of support also remember that you harassing enemy laners with auto attacks for the additional gold and for the purpose of taking their without your adc having to risk their own health or their CS.

Get to the Tear and begin spamming abilities to build up its passive so that once you get towards the Archangel Staff you can evolve it into the Seraph's Embrace.
Always keep wards up in the river bush during the laning phase and keep all three wards from your Ruby Sightstone.
Once you get your core items you shield be a complete mennance in team fights with you ult, stun and heal,

Pros

Great heal
Useful damage
Speed increase on spells
great team fight potential

Cons

Soft early game
Abilities move slow

This is a preference, I love flash and since Exhausts nerf and the heal buff, heal helps greatly in both the laning phase and in team fights. Don't be afraid to use heal early in team fights before the ignites are thrown out same principle applies to laning, but also using it at extremely low health can make surprise the the other team and turn a fight in your favor.

I play all of my champions aggressively and if you find yourself not comfortable with the guides that have you playing soft most of the time then hopefully this helps you out, also keep in mind that many adc prefer the cautious route as well. Please comment if there is anything you would like for me to add.