There is a famous saying for dads that their children need to see their dads love their moms.
That is a good start.
Children need to see their dads love their moms love their dads and their moms love their dads.
Also, respect, support, encourage each other.
Both parents, married to each other or not, need to model and show their children what a healthy, happy, kind, giving, game, fun, loving, playful, supportive, encouraging, affectionate, collaborative marriage looks like.