The 2 most important things, these account for 98% of whether you succeed or fail in your body composition goals

1) Eat the correct number of calories:

Find your BMR, basal metabolic rate, the amount of energy it takes to maintain/sustain your bodyweight. For men, it's your body weight x 14, 15, or 16(depending on activity levels) in calories. For women it's 13, 14, or 15.

200 pounds x 15(moderately active but don't do manual labor for a living) = 3000 calories to maintain your body weight. Going on a 500-700 calorie deficit is sustainable for a decent amount of time.

The smaller the person, ie a 125 pound inactive woman would have a bmr of 1625 (125 x 13= 1625), the smaller the deficit, 200-400 calories would be plenty.

Eating at a small to moderate deficit will help you make sustainable changes in your eating habits and you won't suffer. If a person wants to gain quality muscle without crazy amounts of body fat, eating a surplus of 500-700 calories works pretty well. If you want to go for broke and you're young, say under 35, you can go balls out and eat like 4000-6000 calories and you WILL build tons of muscle but also gain fat(which isn't hard to lose if you know how).

2) Eat enough protein:

Anyone doing resistance training(which should be everyone) needs .6-.75g of protein per pound of body weight. 150 pound person needs 90-122.5g of protein per day. This can be spread over 3, 4, or 5 meals, it's not very important, probably not a good idea to eat 2 meals or 6 meals, but overall protein and calorie targets for each day are most important.

Obviously try to eat foods and not products, but the ideology/agenda people are mostly full of shit and will just give you hurdles that make it tougher to comply.