How to Preheat an Oven

Before you bake something, your oven needs to be heated to the proper temperature. While it takes only a few seconds to turn on your oven, it can take several minutes for your oven to reach the right temperature. This is why it's often best to start the oven during the beginning or middle of your cooking, instead of waiting until the end. That way, the food will be ready faster.
Steps:
1. Open the oven and look inside to check that nothing else is in there. If items are found in your oven, remove them so they don't get damaged by heating.
2. Check what the preheat level is. Turn on the oven and set to that temperature.
3. Wait until the oven reaches this temperature before placing food in.
4. Most modern ovens have a setting that lets you either see the current temperature or beeps when ready. If you have an old style oven, best bet is to wait 15 minutes to allow the oven to be fully heated.
Tips:
1. If the temperature gauge of your oven does not work, or works improperly, you can purchase an aftermarket one from your local hardware store that just hangs inside the oven.
2. For older-style ovens, place the item in the oven and extend the cooking time by approximately 10 minutes.
Warnings:
1. If you don't wait until oven is fully preheated, food can take longer to cook, or cook unevenly.
2. Don't open the oven door, just to check. You lose a lot of heat every time you open it.