Why do you need to transition?
In all seriousness, you do not NEED to transition smoothly. However, by transitioning smoothly your body gets used to the added caloric intake slowly and therefore deals with it better. This helps keep off initial fat gain by sticking to a maintenance schedule for about 2-3 weeks before taking starting in on your bulking diet.
It is extremely important to transition smoothly if you removed something like carbs from your diet (like I do), and are reintroducing them back in for your bulk. By adding in carbs slowly and smoothly, you do not rebound and gain 8 lbs back overnight. Your stomach will thank you for not assaulting it with a nutrient that you did not give it for the past 5 months. Try not to confuse your metabolism fully.
First off start by slowly adding in whatever macro-nutrient you decided to cut. If your carb intake for cutting was under 100g/day, bringing it up to 150g for the first 7 days is safe and effective. Then the next week bring it up to about 200g or to around 1 gram per pound of bodyweight. I would also advise your protein intake to be around 1 gram per pound of bodyweight, if not slightly higher. As for fat, about 0.5 grams per pound of bodyweight is sufficient.
Calorie Count Second
As for the calories. Add in about 500 for each week until you hit your calorie goal for bulking. So if you were at 2000 calories a day while cutting, go to about 2500 for the first week after you finish cutting, and then 3000 calories for the following and so on. Try to be around roughly 750 calorie surplus, and try to time your biggest meals around your training. Happy bulking.
No, it is not an exact science, and takes a little bit of playing around with what works for you, but this is how I do it.
Success is voluntary.