Check the Air Filter
A badly clogged air filter can cause the furnace to overheat and shut off, so replace it if it's dirty. It can be hard to tell with some filters, so consider installing an air filter gauge that lets you know when it's time to replace the filter.
Check the Power
Make sure the power is on! The power switch for your furnace looks like a regular light switch and can get bumped and turned off accidentally. If the switch is off, just flip it back on. See more simple furnace fixes you can DIY.