This is my sona guide how I play sona. This guide works for me and i wanted to just share the information with you. I find that some people who play sona are just too squishy, they dont get any kind of health and the enemy team just targets the sona and then its like playing 4v5.
This guide works for me.

Seal of replenishment:- I get this because Sona uses a lot of mana she is constantly healing, speeding and attacking. If sona doesn't have this rune i find it very difficult to be a good support.

Greater Glyph of Focus:- I this because i think that Sona needs to be able to spam her spells like crazy. she has to be constantly with her team healing all the time. This rune help with that a lot.

Greater mark of focus:- I get this rune because of the same reason as the glyphs just some more cool down for yourself which then helps the team.

Greater quintessence of replenishment:- Same reason as my Seals mana repleishment is very important.

Flash[/b] Very important because if your team fight fails then you want to be able to get out of there. I pick this instead of ghost because 1. I already have a speed and 2. you can use flash over walls for the ultimate escape. Flash can also be used to attack, flashing in and then using your ultimate is a great way of surprising the opposing team and getting a kill for your team.

Clairvoyance Clairvoyance (CV) is very good for checking where the opposing team is all the time. you can use it to set up fights and just making sure things are safe