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It's best to cut back overwintered plants to the base of the stem in the spring. Montauk daisies may become woody if they don't die back to the ground each winter.  Cutting them back prevents the plants from becoming too woody. Pinch the stem tips back to the topmost bud when new growth apprears.  Do this several times in the spring and ealy summer as you would with chrysanthemums to encourage more branching and flowering.  Trimming off the flowers as they fade will also produce more flowers. Divide in the spring when the center of the plant begins to die out, or about every three years.  Dig up the roots, cut out the dead parts, and replant the living roots. I hope this helps.