21. Check your tire pressure
Your tire pressure matters more than you probably think it does. Not only is it unsafe to be driving with significantly under- or over-inflated tires, but it can also cost you in fuel-efficiency. The folks at RightPSI.com have noted that by keeping their tires properly inflated, drivers can save up to $65 per year on gas and about $5 per year via making their tires last longer. So go buy a simple plastic tire-pressure gauge for a dollar or two or a fancier digital model for around $10, and check your tires regularly. At a minimum, have your tire pressure checked whenever you get an oil change or any other auto servicing.