Three workouts per week on non- consecutive days will show the best improvement. If you add intense weight training, this amount can climb to 1.2 - 1.6 grams per kg body weight. However, the regular consumption of protein in the U.S. exceeds the recommended daily amount for regular or body building needs, so most people don't need to add more protein-rich foods to their daily intake. Plants supply incomplete proteins, but by eating various plant groups, a person can get the amino acids they need. By no means do these have to be eaten at the same time, or in the same meal, but they need to be eaten sometime during the same day.
Soy protein is complete by itself.
As a general rule, legumes and grains and nuts and grains provide you with complete amino acids. So will eggs and milk products. If you're a traditional American eater, you probably don't need more protein in your diet, since Americans usually get way more than they need. Eat a variety of foods at meals and in between. Have fun bulking up the healthy way.