What EasyEJL said is basically what it comes down to, it really depends how anti bad weight you are.
If you are very anti, start adding 200 to 400 calories per week to your maintenance. Try and make this from a protein source where possible. If you gain more than 1-2 pounds in a week you are over eating and will be gaining fat, if so knock the calories back by 200-400. When you stop gaining strength and size, add another 200-400, repeat. You have to be mighty patient to lean bulk tbh, its not for everyone, including myself.
Make sure your macros are balanced, between .4g - .6g of fat per pound of body weight, 1g - 1.5g of protein per pound of body weight, closer to the top end of the targets whilst bulking. You need fat, do not avoid it because you are aiming for lean gains. It balances hormones and provides a slow release energy source, just make sure they are good fats.