As I write this the temperature is dropping, with frost predicted tonight and tomorrow night. Gardeners in cold-winter parts of the country have a different relationship to frost than we do, I think. In Indiana, where I grew up, frost happened, and then we had several months in which the only green outside was the dull, dark green of wintering needleleaf evergreens--the spruces and the pines and the like. If you wanted to see a flower, you could go to the florist's. (And I often did, to get even a single rosebud and bring it home to draw or paint.)
In Indiana, where the temperature was generally well below freezing for several winter months, you might try to save some annuals if the frost was early in the fall, but once winter was underway, plants lived or they didn't. I suppose there might have been horticulturists somewhere who wrapped slightly too-tender plants in burlap and tried to get them through the winter, but no one we knew did any such thing. We grew plants we knew were hardy enough to survive, even if they died back to roots each winter, we let the frost do its work, and we waited for spring.
But here in the Bay Area, our average winter low hovers a few degrees above freezing or a few degrees below freezing. We dabble in plants that can take just a few degrees more cold than we get in most winters, but not as much as we get some winters, and then, when a big frost is predicted, we worry over them. Which makes sense, considering that if we can get them through these very few nights, we will probably have them for years to come.
So if you have planted stuff that can't take frost, tonight will probably find you out there with bedsheets or floating row cover, draping your plants. It is a good idea to use plant stakes to prop cloth covers away from plants. Cardboard boxes make good covers too, since they form a firm chamber that doesn't touch a plant.
Should plants frost over, and they are important to you, preventing morning sun from hitting them until the day warms them a bit will help them thaw more safely. Don't prune plants that are damaged for awhile. You may find that parts you thought would die will return to health in a few weeks.