If you want to stick with a Selesnya deck start by getting the scry lands from Theros block and the new fetch lands from Khans Of Tarkir. You can also get the new dual lands that give 1 life. If you want to power up your Seraph more you could go with a token deck. Things you could consider : Ajani Steadfast, Nissa Worldwaker, Hornet Nest (to go with Hornet Queen), Preeminent Captain (only if you have many soldiers in your deck), Spirit Bonds, you could also get some removal like banishing light. Spear of heliod, Elspeth could also be good. You could also consider Dictate Of Heliod. If you really want to go only with tokens go mono white. I also have two selesnya deck in my profile (standard) if you want to check but also all the cards will rotate in october.