The 70/30 Rule
One way to avoid sticking is to grill salmon fillets, flesh side down first, for about 70 percent of the total cooking time.
Roll the fillets over with tongs when the flesh releases easily from the cooking grate. Finish cooking them for the remaining 30 percent of the cooking time.
Slide a spatula between the flesh and skin to scoop the fillets (without the skin) off the cooking grate.