Not too long ago, I weighed 55 Kg, as a 5'10'' specimen. I flirted with being underweight, and yes, everyone but me saw me as skinny.

So I increased a bit of my protein intake and began light workouts- 20 pushups, cycling and jogging on Saturdays, etc.

Now things are better now.

Great tips, by the way. Well-researched, well-written, and very insightful. Keep it up.