I'm sorry to be the one to tell you this, but there are no strict laws of nutrition! When you start to lose or gain weight you don't get a handbook with a long list of do's and don'ts.
You're left to do your own research and find your own way, but this isn't a bad thing! It'd be a boring world if everyone did everything the same way.
Having said this, I'm still going to give you a head start with some of my personal 'laws' that might help construct your very own way of dieting!
1. There are SO many diet types and eating styles which can cater to you, your lifestyle and preferences. Not that you have to follow a particular style, but just to name a few we have low-fat, low carb, keto, intermittent fasting, low GI, paleo etc. which can ALL be similarly effective for improving body composition, it just depends what your personal preference is.
2. Fat loss is not driven from what diet type or eating style that you select from the above but is instead governed by calories and driven by a sustained caloric deficit created either from your diet or exercise.
3. For fat loss, those starting with a fairly high percentage of total body fat may benefit from a more radical calorie deficit, but NOT starving yourself. Use the BMR calculator here or visit the AG Fitness Training Forum for an instructional video on how to set your own calories! Those that start fairly lean may wish to only put themselves in a slight deficit to help preserve muscle mass.
4. Diets focused on building muscle aren’t necessarily driven by what type of diet and eating style you select but are more so driven by sustaining a caloric surplus and increasing resistance training intensity/volume.
5. Higher than normal protein intakes (in excess of ~2.2g/kg) may result in improved body composition in active individuals with even higher intakes POSSIBLY needed in lean, resistance trained individuals in a calorie deficit to retain maximum lean mass.
6. In terms of body composition, meal timing is of minor importance once total daily calorie/macronutrient intake is achieved. In terms of performance and recovery, carbohydrates and protein both in and around exercise can aid in enhancing performance and recovery.
7. In terms of body composition, food quality is of minor importance in the short term BUT in terms of overall long term health, it is advised to select micronutrient dense whole food sources as much as possible. There's no point in wasting calories on high-calorie foods that leave you unsatisfied. Stick to good wholesome food 90% of the time and your body will thank you for it. Also, supplements may contribute some small benefits but are unnecessary and should never take priority over food and exercise.
8. The long term success of a diet depends upon compliance and adherence, so choose a diet or eating style than compliments your lifestyle. Don't jump on the keto bandwagon because someone at work told you to if you know that you won't be able to sustain that kind of diet. Choose what diet is right for you, and if there isn't one? Make your own!
No matter what you take from these 'laws' of dieting, successful diets all have one thing in common - creating a calorie deficit and sticking to it.