In order for Immortal Servitude to be successful, you need the majority of your creatures to have the same casting cost. For example, run 4x Xathrid Necromancer then the rest of the creatures be 2 drops, that way you can pull all your guys from the graveyard instead of just 1-2. Also, bear in mind that Orzhov Charm works well with Immortal Servitude decks if you chose to do all 1 drops + xathrid.

P.S. Planar Cleansing is bad and shouldn't be played. Merciless Eviction is decent if you want a board wipe in your colors, that way you can kill indestructibles (gods) or you can chose to kill whatever is bothering you, planeswalkers namely. But if you do run a 6 cost card, you need more than 20 lands, more like 23.

Great suggestions. I'll rethink the cmcs of my creatures and will definitely add in some lands. I thought about Merciless Eviction , but that won't kick Xathrid Necromancer for the zombie army I'm shooting for. Though, now that I'm thinking about it, a lot of people are playing indestructible creatures (gods and whatnot), so maybe I should just rethink Xathrid...