Ectomorph muscle gain is the elusive goal for many skinny guys both blessed and cursed by a super fast metabolism that both keeps them from gaining fat but also makes it difficult to put on muscle mass.
There are some things you can do to change hat hardgainer tag to something a little less depressing such as steady gainer or incremental gainer because your genetics can be overcome if you are willing to taker a few tips from the skinny to muscle professionals.
3 Quick muscle gain tips:

• Rest is more important then you think - The body does not grow muscles when you work out.
  It actually does the repair and growth of muscles while you are at rest and especially when you sleep.
  Make sure to get a solid 8 hours sleep a night and do not go to the gym every day ...
  give the body time to heal and you will see greater muscle growth than if you put more gym session in.
  
• Eat more and more times - To combat your fast metabolism you need to consume more calories.
  This will give your body the excess fuel it needs to repair and grow your muscles when you rest.
  By in taking much more food you will give your body all it needs to function plus reserves that if you were not exercising may turn to fat but will be added to muscle if you do workout the right way.
  Also try to break your meals into smaller but more regular intervals to keep the body fueled at all times so it does not cannibalize our muscle reserves.
  
• Lift Heavy - To take advantage of the energy reserves you are storing and turn them into ectomorph muscle gain when you rest you must first stress your muscles by lifting heavy weights to push yourself to your bodies limit.
  Only by lifting your maximum load and trying to go beyond that will you force the body to adapt by slightly damaging your muscles in a natural process that allows the body to repair the injuries and add more muscle mass on top of this to compensate.
  Lift heavy and intensely; there is no point in long cardio periods or lifting light weights many times.