When you think of snug, think of hug. It wraps around you. With smug think of the look on someone's mug (face).

hi Dinghui, the best way I can think of to remember them is that "snug" is related to a verb "snuggle" which means to either get comfortable and cozy in like a bed or sleeping bag, or to hold another person close in an affectionate embrace -- so snug is the way you feel when you are snuggled :-) You could associate "smug" with "mug" which is usually a cup, but is also a term for someone's face, like a mug shot. We commonly say someone has a smug look on their face, related to what Jose said, they are too sure of themselves.

Snug is about clothes or some material that fits around another material that fits tightly. Snugness is the tightness of that fit. Smug is when a person is too sure of themselves in some decision and you want to slap them in the face :-).

snug - snuggle- cuddle smug- smug look on their face - ‘mug’ slang for face