An easy way to make sure your bike is in good working order is to do an ABC Quick Check.
Air: Be sure you have enough air in your tires
Brakes: Look to see that your brake pads are not worn, and that your handle brakes are properly adjusted. You should be able to slot your thumb between the handlebrake and the handlebar when fully squeezed. If there's not enough space, adjust the brakes.
Chain and Cranks: Pull on your cranks to see that they are not loose and look to see that the chain is not rusted and it is free of gunk.
Quick Release: Make sure all quick releases are closed
Check: Take a slow brief ride to check that your bike is working properly