When bottling, I add the priming sugar into the bottling bucket first, then I siphon my wort into the bottling bucket using a tube long enough to coil (at least a little bit) on the bottom of the bucket. This helps mix the the priming sugar into solution. I had inconsistent carbonation on some of my first few batches and this approach has worked well for me.
Do your best to control fermentation temperature, and remember you're worried about the temperature of the beer, not the ambient room temp. The beer will be warmer than the ambient temp., sometimes by 5-10 degrees which makes a big difference.