• Use either the frost cloth you buy at Home Depot, or old bedsheets. I've used both, and bedsheets work just fine. Just never, ever, use plastic.
• Put the frost cloth on after it gets dark, and off at sunrise. Keep an eye on the forecast. If it's gonna get to freezing or below, go drape the frost cloth over your plants. You don't need to be neat. Then when the sun comes up, take off the frost cloth right away. Your plants need the warmth of the sun, and as much sunlight as they can get!
I only have tender tropicals in my backyard, which means that I can go out the last thing at night, and the first thing in the morning, very quickly. I also have these plants in areas that are as protected as I can get them, not out in exposed areas. Under an overhang is best, like this area, which is under a tree. And it's best to keep the area crowded, as plants do better when they share the warmth of each other.
It's December 3rd and it's really too early to start worrying about it, but I have put the frost cloths out on the patio, to be handy when it really does start getting really cold. If you have new plantings, especially of cycads, you will want to give them more protection than the older plants. It does no harm to put the frost cloth on at night, so if you're not sure, go ahead. After many seasons you will be able to cut it closer, and many years I haven't used frost cloth at all.