Add me if you want.
as for build guides: avoid mobafire.
solomid is much better!
for build, i start
2
1

then i rush
which, if you poke a lot, should be available at first back.
As you get
, you exchange
for
!
After that i build
.
depending on how well you manage your mana, you decide which part of
to build first,
for mana or
for more poke potential. After you finish
you should work on boots. depending on your play-style,
or
.
are a good choice too but i value the mpen of
or the mobility of
over the CDR of the
.
You could go
now, but i usually don't do that much anymore. If the other team is itemizing MR, i go
, if not i go
.
While you are squishy AF, your mobility through boots and your E should alow you to dash in and out, applying Q and Powerchord poke damages.
With some AP, your heal potential is ridiculous.
For Summoner spells i always get
.
Sona is an aggressive poke support and when you see a low health enemy (preferably one of their carries), using
Q, Powerchord and
often secures a kill and leaves the other team wondering why a support does damages!
If you feel that you need a tanky item
is a great choice. it finishes off your 40%cdr, increases your self healing by 20% and gives you health regen, Health and MR.
Last upgrade to
and also to 
Dont forget that there are elixirs to chose from too:
and
or if you know you are going to hardcore push, especially with baron buff go 
Dont forget that your powerchord can be applied to structures, so while you are auto-attacking towers, spam spells (3rd must be Q) to get that powerchord onto every 3rd auto-attack!
in lane advice, dont be scared! YOU are the bully. Your Q has quite a reach and favors Champions in range over minions.
Every 3rd spell you have a Powerchord on your auto-attack, which does different things depending on which spell you cast last.
Read up on that and procatice applying that.
Using the powerchord correctly is the difference between a good sona and a buttonmasher.
I do not take exhaust because your W activated Powerchord is an exhaust in itself on a lower cooldown!
Play her aggressively. it's more rewarding, more fun and has a higher impact!