Paint the furniture with an oil-based primer. If you then use paint over the primer, you may need to reapply now and then, as paint on wicker tends to crack because it is so pliable.
Clean your wicker furniture regularly because it has a lot of spaces for dirt, dust and debris to collect.
Dust the furniture often if kept indoors. A soft cloth can work well for indoor furniture, or you can use a brush attachment for your vacuum cleaner, which will loosen up the dust and suction out any debris hiding in the crevices. Outdoors, a stiff brush can be used to remove anything that has collected between the strips of wicker.
Keep your furniture dry when possible, rather than cleaning it with too much water or liquid cleaners, because wicker absorbs moisture. This can lead to warping, and wicker can take a long time to dry if you get it soaking wet.
Wipe the furniture down with a mild solution of ammonia and water if there is mold or mildew. Wipe this off with a damp cloth immediately, and then dry it with a dry cloth or sponge.