We're taught very young to remember our ABCs, and that's no different when it comes to bike maintenance. It's normal to leave your bike unattended during the winter when the riding is less than ideal. Thankfully the League of American Bicyclists created an "ABC Quick Check" to help you before your first ride in months.
We are starting at the top of the alphabet with A. You must check the air in your tires before you even attempt to hop on the bike; if there's no air, you're not going anywhere. Inspect the tires by squeezing them. If they don't feel hard, check the air pressure using a pump with a gauge. Inflate your tires based on the recommended air pressure of the specific bike you're riding. After that, double-check that there are no other reasons your tire may go flat, such as cuts, bald spots, holes, or cracked sidewalks. If so, it's best to replace them!
Next up is B - Brakes. The brakes are essential not only to your bike but to your safety. To check your brakes, spin both wheels forward to ensure that the rims aren't rubbing against the brake pads. Squeeze both brake levers to ensure that they are an inch of space between the lever and the handlebar. If your brake pads have less than a quarter-inch of rubber left or touch the tire or spokes, the pads need to be placed.
CHAIN, CASSETTE, & CRANK
Finally, the three C's, chain, cassette, and crank. Your crank and chainring bolts should be tight. Also, rotate the crank to make sure the chaining is straight. Depending on how often you ride, it's essential to lubricate your chain every 5 - 10 bike rides or every 100 miles.