Use a leave-in conditioner with sunscreen (at least SPF 30) every day. If you go in the sea or a chlorinated pool, wash the chlorine/salt out immediately and replenish the conditioner. Wear a straw hat if you are going to be in the sun for a long period. Use a colour-correcting shampoo or conditioner whenever needed (for me about every 3 or 4 weeks). Don't over-wash the hair.
But most important of all - wear the hair, and don't let it wear you. These things are cheap enough to be regarded as disposable now. If you unexpectedly end up at a nice beach and you haven't brought your hat or your conditioner - forget it. Plunge right in. Don't let wearing a system hold you back.