Here are some tips to start building muscle today.
Pump Up With Protein
Because muscle fibers are made up of many different proteins, protein is the #1 necessary ingredient to build muscle.
One study found participants who ate 20 grams protein every 3 hours significantly increased muscle building potential, compared with those who ate 40 g every 6 hours.  So, eating good amounts of protein throughout the day feeds muscles and keeps them raring to go.
The ideal daily protein intake is about 1 g protein per pound body weight.  So, a 200-pound man should eat about 200 g protein a day. Of course, this differs depending on individual needs.
The best high protein foods to eat are chicken, turkey, fish, lean beef, eggs, beans, nuts, milk, and cheese. 
Many bodybuilders also use protein supplements, which provide a heavy dose of pure protein. Whey protein powder is generally the best choice because it has high protein content and lots of muscle-building branched chain amino acids. 
Be careful, though. Protein shouldn’t make up more than 30% of your caloric intake. Too much protein increases risk of kidney problems, dehydration, and other issues.