Be prepared to lift the resin furniture. If you're physically unable to lift the furniture, ask someone to help you. But be sure they can be available on short notice.
Watch the morning weather report or look up your local weather online. Make sure you find out what the weather's going to be like in the early morning. Around noon is when the sunlight will start to be more direct and potentially damaging to your resin furniture.
Move your resin furniture into the shade in the morning if the weather report says it's going to be a particularly sunny day. For the most part, resin furniture can be stacked and stored easily. Have a designated area in your garage or outdoor shed where the resin furniture can be stored during sunny days.
Consider keeping your resin furniture in the shade to protect it from the sun. If you have a shady area of your yard or a covered porch, you can protect your furniture from the sun simply by keeping it in the shade.
Have a cover that you can use to protect your resin furniture from the sun. You can use a furniture cover, large blanket or tarp to protect your furniture. Try to make sure every surface of the resin furniture is covered to minimize sun damage.