The Maillard reaction is the chemical process that occurs when amino acids and sugars are exposed to heat above 285°F (140°C). It's what gives seared steak its crust, roasted vegetables their sweetness, and bread its golden color.
Dry your food thoroughly before cooking — moisture creates steam which lowers surface temperature below the browning threshold. Use high heat and a hot pan. Don't crowd the pan; crowding traps steam.
Pat chicken dry before roasting. Let steaks sit uncovered in the fridge overnight. Roast vegetables at 425°F or higher. Use butter for extra browning compounds (milk solids brown beautifully).