OK so in short in order to gain muscle we have to be in caloric surplus, how big or how accurate that surplus matters.
To successfully bulk with putting on as minimal fat as possible we still have to mindful of our intake. In order to achieve this lets go through the breakdown.
1). Slight Surplus
So in order to creep our weight up slightly we want to eating around 200-300 calories over our maintenance. This will hopefully put you in around the 2-3lbs per month rage.
I want you to understand that in order to build, maintain and sustain muscle we must give it a reason to stay or grow. That's the nature of a lifters career, every heard the term "use it or lose it"? That is exactly what we are doing here. The training that built your body will be the training that you will use in order to lean down. I recommend that you stick to compound movements as the main focus along with training in both rep ranges of hypertrophy and strength.
There's subtle tweaks to the macros and that is highly individualized. Mainly we are either reducing carbs and fats to cut or increasing carbs and fats to bulk. Again it's going to differ per individual, you'll have to figure out how much fuel is necessary for your workouts along with hitting your composition goals.
This macro stays constant for the most part, there is a range though if you want to be more flexible. The leaner you are the higher your protein intake can be as your body is more adaptable to utilizing protein. Contrary to belief we do not need as much protein while bulking as whenever we are in a surplus the body is not as optimal in using this macro as a resource.
2). Eating Sufficiently
OK so eating food may not be enough, we have to be mindful of what the calories are broken down into, how much protein, carbs and fats does matter on your composition. You will have to determine how to creep these numbers up slowly.
Of course tracking your calories, we have to watch the trends as stated in number one, keep an eye on gaining the right amount of weight over time. 2-3lbs per month should do it.
This is still being mindful so we are being restrictive and not going out and partying just because we are in bulk mode.