The sweet spot for LGD seems to be between 8mg and 16mg, depending on how responsive you are and how clean/healthy your receptors are.
If this is your first SARM cycle you'll probably be able to make decent gains with 8mg, but if you're a seasoned SARM/PH/AAS user then you'll probably need to dose further towards the higher end. My suggestion would be to start lower and work your way up from there.
What are you running as your Test/DHT base?