Fizzles and backfires are normally caused by trying to cast a spell at too high a level. When you look at your spell choices the color of each circle tells you how well you can cast it. Green is good and red is bad. Best option when you don't want the problems is to cast the highest level green/lt green spell you can.As your realm skill, professional level and school skill rise, the circles will get green on higher power levels.
A note: do your best to save some spell picks for later in the game. Most spells are available by finding/buying/stealing books but the 7th level spells are only available via spellpick at level-up.