3: Get ample fats
One mistake people make when trying to keep lean is to avoid fat as much as possible. That is a bad idea for numerous reasons. For one, there are essential fats your body needs, such as omega-3 fats from fatty fish like salmon. These fats have recently been found to be critical players in muscle recovery and growth, as well as keeping body fat off, aiding joint health, protecting from heart disease, boosting brain function, and a host of other health benefits.
Then there is monounsaturated fat. This is not an essential fat, but it is a healthy fat due to the fact that it provides numerous health benefits and is readily burned for fuel rather than being stored as body fat. On top of that, research shows that male athletes consuming more monounsaturated fat maintain higher testosterone levels. Actually, the research shows that male athletes consuming more monounsaturated fat AND saturated fat maintain higher testosterone levels. Yes, you actually WANT to consume some saturated fat (albeit in lower amounts) versus trying to avoid it at all costs. Good sources include beef, dairy (full fat or reduced fat, but not fat-free), and whole eggs.
The only fat that you want to avoid as much as possible is trans-fat.
The simple rule for fat intake is to consume 40% your bodyweight in pounds (or about your entire bodyweight in kg) in grams of fat. So, if you weigh 200 pounds (90kg), you would consume about 80 grams of fat per day with about 40% being monounsaturated fat, 40% being polyunsaturated fat (mainly omega-3 fats), and 20% being saturated fat each day.