During pregnancy, your intake on average should be increased by 300 extra calories.
On average, weight gain of 20-30 pounds is ideal (0-5 pounds in the first 12 weeks, and ½ pound-1 pound a week after that). Some patients may gain more than this and some patients may gain less, but the key is to eat a healthy balanced diet. Especially during early pregnancy when nausea can be significant, eating small more frequent meals can be helpful to prevent heartburn and maintain an even glucose level.
Eat what you enjoy, but make healthy choices with minimal amounts of fats and sweets to prevent excessive weight gain and possible gestational diabetes.