“Luminous, O monks, is the mind. And it is defiled by incoming defilements” (Pabhassara Sutta, AN 1.49-52).
“By effort and heedfulness, discipline and self-mastery, let the wise one make for himself an island which no flood can overwhelm” (Dhammapada 25).
One particularly useful type of meditation is visualizing a castle wall around the mind, or that the mind is on a high mountain (perhaps an inactive volcano) on a deserted island, or something similar. Outside the wall is the din of the dualistic world: sounds, sights, thoughts and feelings that have arisen automatically/karmically, etc. bombard the mind’s peacefulness. Inside the wall is completely silent and still, as close to a nirvanic state as possible. Especially in noisy, stressful environments, this meditation can be very soothing.