1 Less is more
Ectomorphs have a very fast metabolic rate and as a result they need to exercise less in order to prevent their bodies from burning out their muscles. The less the Ectomorph exercises the faster he grows. 3 days per week is optimum for Ectomorphs.
2 Stop doing cardio
Cardio slows down the body's recovery especially for an ectomorph, who burns fats and muscles very quickly. For optimum growth an ectomorph should stop doing cardio completely or keep it at once a week if it's a must.
3 Never stay hungry
Ectomorphs process food faster and as a result they run out of nutrients fast. For optimal growth ectomorphs need to keep supplying the body with nutrients every few hours. Eating 5-6 meals a day is strongly recommended for ectomorphs.
4 Lift heavy weights
Ectomorphs must list heavy weights in order to drop muscle mass. Using light weights will usually result in fat burning instead of muscle development.
5 Must get plenty of rest
Ectomorphs must get plenty of rest for their bodies to recover. They should do nothing on the day that follows their training day. It's strongly not recommended for an ectomorph to train for two consecutive days.
6 Consume plenty of carbs
Ectomorphs need a constant supply of carbs to provide their bodies with energy to replace the energy they burn. Ectomorphs must focus on getting a constant supply of carbs throughout the day, in addition to protein. (See What are the characteristics of an ectomorph body?)
7 The exercising session must be short
For an ectomorph, the shorter the exercising session the better. The optimum is 45 minutes, but under all costs the exercising session must not be very long or else it will result in muscle loss.
8 Focus on Ccmpound exercises
Compound exercises such as chest press & squats can help ectomorphs stimulate many muscles in shorter periods of time. This can lead to shorter exercising durations and consequently, more muscle mass.
9 3 sets per exercise
An ectomorph should not do more than 3 sets per exercise. To achieve the goal of growth the ectomorph must not over-stimulate his muscles in order to not get reverse effects.
10 Shouldn't think about shredding during the growth phase
During the growth phase the Ectomorph must eat as much as he can. It's almost impossible for an Ectomorph to achieve both muscle growth and shredding at the same time. (See How to strengthen your core muscles?)