The deck itself looks good but I do see some areas that you might want to tweak;
1) Since you're playing rakdos (B/R) you're gonna want to play creatures and destruction spells that hold a big sway over the course of the game.
Sleeper agent you don't really want to use in this deck because even though it's one mana you are giving your opponent a 3/3 creature to attack you with next turn. The
fulminator mage would best
serve as a sideboard because playing a creature just to blow up a land is a waste of a creature, especially when you could just play
volcanic upheaval or
demolish. Lastly are the lands that you have chosen, try using more basic lands and less of the ones that deal you damage. Playing
bloodfell caves would
serve you better because you're increasing your life and still getting the same available colors.
2) As far as cards for improvement try adding some of the creatures from the rakdos guild (in the return to ravnica block) and some of their low drop spells to help your
monastery swiftspear. The creatures from the guild have varying effects whether it be first strike (
splatter thug),
regenerate (
grim roustabout), and even damage effects (
hellhole flailer). You should try looking into to those, i guarantee your game play will see some improvements.