If you are cooking more than one thing, put them on different racks -- or even separate ovens if you have a double oven. If you're using one oven, position them so that the one on the bottom rack isn't blocking the heat for the item on the top rack.
You may have seen a Pinterest tip that suggested lining your oven with foil is a great way to protect your oven from drips. Just don't do it. Not only can the reflected heat make your baked goods cook faster, it can damage your oven.
There have even been reports of the foil melting, and the heat reflected off of the foil may burn out the oven's heating elements. Instead, use a silicone oven liner that is designed to be put inside an oven.
If you leave drips and crumbs on the bottom of your oven, you could be sabotaging your baking. Those food bits can catch fire or smoke, which can overheat the oven, or at the very least may make your baked goods taste like soot.
The self-cleaning option on your stove is a great way to keep it clean, but beware: it only cleans up to a point.
After the oven has cooled down, wipe the interior down with a damp cloth to remove any soot, and leave the door open for a few hours to let the oven air out. Skipping this step might make your next batch of cookies taste like a house fire.