You need a good knowledge of what the decks you are facing are doing to side board efficiently with this deck. The main deck will hold out against most things but certain decks really hurt us and there will be cards that are useless in main deck against some decks. For example, Anafenza is a dead draw for us against Scapeshift, so swap in Spellskite/Eidolon/Aven for it.
Abrupt Decay: We don't really have efficient ways to deal with planeswalkers and some enchantments/artifacts or against counter spells, helps against those.
Anafenza, the Foremost: Check Creatures panel above
Aven Mindcensor: Tron, Valakut decks (Bring to light/Scapeshift/Primeval Titan), Chord, etc. Lots of uses. Also against cards like Surgical Extraction, Crumble, etc
Eidolon of Rhetoric: Combo decks, burn decks, or just decks that like to cast a lot of stuff each turn... Keep in mind that Eidolon looks at the whole turn, not just after it was played. So casting it also means that is your 1 spell this turn so try to cast it as your last spell on your turn.
Fulminator Mage: Helps against Tron, Valakut, Man-lands
Languish: Against Elves, Merfolk, tokens, etc
Reclamation Sage: Check in Creatures panel above
Relic of Progenitus: Great against things like Tarmagoyf and other graveyard decks. Also useful against decks that use Snapcaster Mage.
Scavenging Ooze: Graveyard hate again... (this may be replaced for something to help with burn)
Sin Collector: For facing decks that have a lot of instant/sorcery spells.
Spellskite: Burn, creature hate, enchantment decks, etc. This card can be extremely useful.
Stony Silence: Man I wish I had a way to search for this against affinity....
