Check with your local nursery for tips on your plants in your area.
cover with sheets or old plastic shower curtains. They make cheap plastic tarps that work just as well.
Do you know what zone you are in? Here are a few sites go get you started.
I am in zone 9 and even though it is hot most of the year, we still get a few days here and there where it gets chilly and even down into the teens for a couple nights, not for long though. When it is anticipated, I cover everything I can with old sheets like tents.
It really depends where you live,how cold it gets,what the plants are,if they are in ground or containers.Don't use plastic the plants will just burn thru it unless it has cloth backing like an old table cloth put the cloth side on plants or you put sheet or blanket then plastic over it. Just use old sheets or blankets and drape over plants secure with clothes pins or big black office clips then remove when sun is up. Some plants you can spray with garden hose off before sun comes up.