Aim to add about 5 g of fiber daily until you reach your goal.  Adding too much fiber too quickly can result in some gastrointestinal stress like loose stools, constipation, painful bowel movements, bloating or gas. Keep track of how much fiber you're eating and how much more you need to consume by keeping a food journal or using a food journal app.  These can help you tally up your total fiber intake each day. Incorporating more fruits and vegetables into your diet will add fiber.  However, if you eat the skin on many fruits and vegetables, you can maximize the amount of fiber from that food.  For example, don't peel apples before you eat them or if you're eating potatoes, try to leave the skin in the dish (such as if making baked or mashed potatoes). Eating fruits with seeds is also a great way to consume more fiber. Berries are among the highest in fiber due to their miniature seeds that are consumed when eating them whole. Whole grains offer more fiber to your diet.  Slowly swap out any refined grains you eat with 100% whole grains.  Try 100% whole wheat pasta or pasta made from brown rice or quinoa.  If you don't like the taste, mix it with a little regular pasta. Have brown or wild rice instead of white rice. Alternatively, try some barley, quinoa or millet. Instead of white bread products, use 100% whole wheat bread.  If you like to eat toast in the morning, make it whole wheat bread. Alternatively, there are brands of bread and English muffins that have 5 or more grams of fiber per slice. Check to make sure processed foods like bread or pasta are 100% whole grain by reading the food label.  The first ingredient should be 100% whole grain flour.  No other refined or enriched flours should be listed. If you can get a fiber-packed breakfast routine going, it may help you easily reach your daily fiber goal. If you don’t like the taste of these, don't worry; you can mix in half a cup of bran cereal with whatever other cereal you like.  Eat a cereal with 5 or more grams of fiber per serving.  Read the food...

TL;DR in Vietnamese:
Bổ sung chất xơ vào chế độ ăn một cách từ từ. Ăn rau củ quả còn nguyên vỏ. Thay thế ngũ cốc tinh chế và chế biến sẵn bằng sản phẩm ngũ cốc nguyên hạt. Ăn ngũ cốc nguyên hạt hoặc ngũ cốc giàu chất xơ vào buổi sáng. Chế biến hoặc chuẩn bị thức ăn và công thức nấu ăn với các nguyên liệu giàu chất xơ. Chọn món ăn nhẹ giàu chất xơ. Chuẩn bị công thức nấu ăn từ nhiều nền ẩm thực. Cho rau củ đông lạnh vào súp. Cho hạt lanh vào sữa chua. Cho một số loại quả mọng vào nước lắc bổ sung protein.