Well, the first question would be, how tall are you and how much do you weigh? People are born with certain genetic predispositions and there's only so much you can or want to do about that. So I ask because are you severely underweight, or you just want to look better? If you are severely underweight, it's unlikely to be high metabolism. It would have to be unhealthfully high to do that. So if that's the case, have you seen a specialist to find out if something is off with you? Have you been tested for nutrient levels? Being thin isn't a bad thing health wise, some studies though they have been challenged somewhat have shown that at least in mice it appears undereating extends lifespan. Doesn't mean it does in people, or that the study was conclusive, it appears not to have been, but it does stress the difference between appearance and health. Which is to say, the easy way to gain weight, and I believe you put this in a prior thread, is to eat more. The more unhealthfully you eat, the more you will gain, such as eating a ton of sugar and fat. One way to have a better appearance without trying to just gain weight by overeating is to do muscle training. While you won't get wider this way, you will get larger muscles and get a good workout along the way, and muscle can make thin look more bulky. But if nothing is physically wrong with you and you're just a thin but healthy person, be careful what you wish for, but again, if that's the case, just eat a lot more and make sure it's fattening food which won't make you healthier but will make you larger.