Cuttin and bulking have basicaly the same ratio protein/carbs/fatintake (around 30%/40%/30%). The main difference is that you eat more when bulking than cutting. Instead of 2500 let's say for an exercising male, you'll take in around 3500, maybe more. Some people believe that ratios aren't as important for bulking but it's crucial in my opinion to reduce the fat gained.
As to when to bulk...that's completely up to your stats. In general, if you're already big, cut. If you're small, bulk.