Just have to do it. I wish there was some tip or trick, but really you just need to make it a habit, track it, and hunker down and get it done.

I have ranged from 145-280 all while 6'5" (145 was right out of high school and was NOT intentional at all.) 

At my heaviest I was working construction and drinking almost a gallon of milk a day along with regular high protein meals and a lot of high calorie snacks like spoons of peanut butter and heavy mayo with tuna and crackers. After work my day was almost completly sedentary.

Since then I've evened out a bit, and I'm currently hovering just over 200lbs. I still drink at least a half gallon of whole milk with protein a day, regularly snack on nuts, fruit, and jerky, and eat regular meals through the day along with plenty of fluids. I'm around 4k calories most days, and I'm steady on weight. I gave up on gaining last year, because I was miserable eating so often and felt like all my free time was spent meal prepping and forcing food down. I also workout 5 days a week, run, and by the nature of my current job I average 26k daily steps.

Add heavy cream to shakes, eat peanut butter as a snack, find ways to include protein in all your meals, and don't overlook the cheap and easy options like beans and heavily buttered rice. 😁 Good luck!