The first thing is understanding why exterior shutters can rot. The sun is your biggest enemy, because it will cause your shutters to contract and expand. If your wood shutters are painted dark colors or black and if they get direct sunlight for most of the day then this is even more so the case. Heat from the sun will cause the shutters to expand and split apart. This will expose untrated areas and the rot process will begin as water and insects make their way into the shutters through these cracks.
By maintaining your shutters, you can prolong their life. Paint your shutters every other year. Paint can fade in the sun and as that layer breaks down over time, the rot process can accelerate. You never want to put an adhesive between a shutter panel and the rails that surround it. Common mistakes are the use of caulk or glue to reinforce the panel. Panels have to have the ability to contract, exand, and shift with changing enironmental temperatures. Th rails and styles are never glued to the panel for this reason and only serve to hold the panel while allowing it some slight contraction and expansion mobility. Paint contractors will unwittingly make this mistake and the overall effect is more harm than benefit. If your shutters are starting to split apart at the rails and panels, you need to do a couple of things. First, you should try to paint any exposed wood that's been untreated. And secondly, you should hammer the rails back in place and reinforce the rails and styles with screws. Never screw the panel to the rails or use glue or caulk.
If possible, don't use the color black. Try to avoid colors with dark pigments in them as they will absorb more heat and reduce the lifespan of the exterior shutters. You can also use a vinyl safe paint or a semi-gloss paint to help minimize absorption from the sun. If your shutters are cupping or bowing, then it's likely that the need reinforcement. Overexposure will do this and a long shutter may need a third hinge in the middle to make it more structural.
Keep in mind, that the sun is your worse enemy. If maintenance and repair are not your cup of tea, then have no fear. There is a no rot solution that does still offer the look of wood and functionality of operable shutters and they don't look like plastic. They're also not made from vinyl. What's nice about vinyl shutters is that they are affordable and they don't rot. The disadvantage is that they will always look like plastic and they too can crack and split over time. They're also non-hingeable. Many people like wood shutters so that they can be hinged and function as operable shutters. You can consider upgrading to PVC shutters, which look just like wood and can be hinged. They're 100% rot free, moisture free, insect free, and maintenance free as well. Window boxes, which are also prone to moisture and rot, are also made from the same material these days. With a little bit of shutter repair and preventative maintenance you can prolong the life of your shutters so that they last twice or three times as long.
