advice for gaining weight

It's really gonna come down to nutrition, even more than working out. First, you'll need to eat at a surplus - more calories than your body needs at maintenance. Depending on how much you want to gain and how fast will determine how much of a surplus you want to consume. 1 pound = 3,500 calories, if you want to be gaining about 1 pound a week, you'll want to be at about a 500 calorie surplus every day (500 calorie surplus per day x 7 days = 3,500 calories). If you want less, eat less; if you want more, eat more. However, you don't want to be gaining more than 1.5-2 pounds per week. Also, keep in mind that if you try to gain more quickly, more of it is gonna end up as body fat. Now body fat isn't a bad thing when bulking and you definitely want it, but the more you add on the longer it will take to get rid of when you start cutting.

For the workouts, you definitely want to lift heavy. Go for the 6-8 reps for your exercises. Those last few reps need to feel difficult. And since you're working a lot of the muscles out to the point of exhaustion (why nutrition is so important!), you'll need to work different muscle groups on different days. Don't go chest day back-to-back.

Let me know if you have any other questions. Go a head and shoot me a message and I'll help as best I can.