Not Updated For Current Season
The masteries shown here are not yet updated for the current season, the guide author needs to set up the new masteries. As such, they will be different than the masteries you see in-game.
This is a build I'm working on for a friend, Scott, getting into the game. Support is a great place to learn and you develop a little of every skill you need to be a great player as you grow. I think Sona is an easy champion to learn the game with and deathly powerful when you master her. I encourage all feedback and please note that the item build order is not set in stone but merely a suggested order. It is extremely specific to help out newer players.
I'll be making multiple guides for my friend to put up on his second monitor here, feel free to use them as you please.
These are a much more offensive set of Runes than you might personally want to run. Armor Reds and Yellows and MR per level Blues are an option; toss move speed or GP10 in the quints if you go the more defensive route. With the Sona nerf she is no longer a champion that can take any real punishment and can only go in at very specific times for poke; otherwise staying behind her carry in the lane or the front line in team fights is wise. This was my thought process going into the runes.
Taric is used as an example of a more defensive support this is also very similar to how I would build Alistar or Nunu.
There is always plenty of wiggle room within any Mastery setup, but this is what works for me on Sona. Play with it as you learn the build/champion and let it evolve into something that fits your play style.
Taric gets the extra gold to facilitate his sustain starting items.
The order of items is merely a suggestion, and one made with the idea of keeping the items simple for a new player. Make sure to build according to what your team needs at the same time as adapting to your enemy.
Taric gets actives earlier and is an example of a more early sustain support that can soak up then regen from damage to open up opportunities for his ADC. He becomes a tanky sort of support that relies more on actives in the mid/late game.
You can chose to max E second over Q if you don't find yourself keeping the Q aura up much, or if you find yourself running/chasing a lot. E will simply synergize better with some teams/circumstances.
The same concept applies for Taric as far as max order, though you can also max Q first if you are being being punished in lane.
Sona gets Heal and Clairvoyance to synergize with her playstyle, and buys Elise's Miracle to scale well with the two. Clairvoyance can be amazing if used correctly to check enemy jungle position, objective status or even to see if a bush is safe.
For Taric the old fashioned Flash and Exhaust often works best. This allows him to move suddenly and shut down an enemy even more effectively.
Pros / Cons
Every support has its place and certain bot lane combos work better than others. I personally enjoy Taric/Graves and Varus/Sona just to name two.
Sona provides heavy sustain with some good poke and escape potential. Her ult is amazing in team fights, and should not be underestimated or wasted. She is however an easy target to burst and has to position well to stay alive and help her team. You'll have to learn the balance between poke and sustain.
Taric is an absolute lane bully but arguably doesn't scale as well into the late game. His stun/shatter combo can terrorize an enemy ADC through the laning phase and his ult can be used to help against objectives or in team fights. He has great sustain when free to auto attack and decent otherwise.
As a support it is very important that you match the pace of your ADC, and I cannot stress this enough. It is your job to match their pace and help them come out on top in the lane.
Personally I generally prefer being a tank while I support and making plays to put my team on the advance. However, Sona has a special place in my heart with her ability to stun an entire team and spam skills that constantly help her team.
The Sona guide is great for many supports such as Soraka, Lulu, Janna and Nami. (ranged)
The Taric guide is great for others like Alistar, Nunu and Leona. (melee)
But of course feel free to interchange between them and come up with a happy medium that fits you!