HOW TO: Calculate your calories & macronutrients
If you're not being intentional with your nutrition, now is the time to start! Download a nutrition tracking app (Cronometer is my favorite) - and make a commitment to use it. A basic kitchen scale ($12 on Amazon) will help you get precise and track accurately.
Tracking nutrition doesn't have to be an every day, forever thing. Start by tracking for just a week. Even a few days. Tracking your nutrition will challenge you to be accountable to the food and beverages you consume, develop healthier habits, and gain a deeper understanding of proper portion sizes.
Proteins: The Building Blocks of Strength and Recovery
Proteins are the foundation of every cell in your body and play a crucial role in building and repairing tissues. Most important to your goals - protein is what drives muscle growth, recovery and maintenance.
Protein, Protein Protein. PRIORITIZE HIGH PROTEIN.
Aim to consume 0.8-1 grams of protein per pound of body weight (if you weigh 200lbs, aim for 160-200g/day) - inadequate protein consumption is the number one reason I see people failing to make progress with their fitness goals. A high-protein nutrition program is a MUST. I recommend supplementing daily with a quality protein powder - two scoops right after your workout or whenever it's convenient during the day.

Carbohydrates: Your Body's Preferred Energy Source
Carbohydrates are your body's preferred energy source. For this reason, many people find that low carb diets leave them lacking energy - especially during their workouts. You can help offset this by prioritizing high carbohydrate meals pre and post workout.
Carbohydrates have become conflated with HIGHLY PROCESSED SUGARS AND FOODS, which are calorie dense, provide us little nutritional value, and often don't satiate our appetite, leading us to overconsume.
With that being said, many people do very well with a low carb (<100g/day) nutrition plan. Experiment and see what works best for you. As long as you're consuming plenty of protein and at least 50g of fats/day, carbohydrate intake can be adjusted to preference.

Fats: Essential for Health and Vitality
Fats play a crucial role in maintaining overall health and hormone production. They are essential for absorbing fat-soluble vitamins, supporting healthy brain function and act as an alternative fuel source for the body in the absence of carbohydrates.
GUYS - restricting healthy fats will negatively impact hormone production and testosterone levels. You don't want that. Keep your daily fat intake above 50 grams.
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Bringing it all Together - Calculate Maintenance Calories
Your TDEE (total daily energy expenditure) coincides with your maintenance calories (daily calorie consumption to maintain current body weight) - they are one in the same.
TDEE CALCULATOR makes it simple to calculate this target. Enter your age, gender, height, weight and activity level - out spits an estimation of your TDEE.If your goal is to LOSE weight... subtract 10-15% and start there.
If your goal is to GAIN weight... add 10% and start there.
Pop that number into your nutrition tracking app and setup your macronutrient targets. Remember, set your protein target at 0.8-1g/lb of body weight, then adjust carbs and fats to preference (just don't go below 50g fats).
TRACKING BODY WEIGHT PROGRESS: Weigh yourself 2-3 times per week, first thing in the morning, wearing boxers or shorts, right after using the restroom. Trend your weekly average.
Aim to lose or gain 0.5-1% of your body weight per week. Adjust total calories (by increasing/decreasing carbs & fats - NOT PROTEIN), until you are losing/gaining at a reasonable, consistent rate.
One more thing... NUTRITION is the primary driver of weight loss or gain. You won't outwork poor nutrition. While you can increase energy expenditure through more activity and cardio, your efforts are best spent dialing in your nutrition - then building from there.