Every time you get on a bicycle, you should check a few things first to make sure it's safe:

• Stand in front of the bicycle, and lock the front wheel in place with your legs or your feet. Then grab the bike by the handlebars and try to turn the wheel. If the bars slip, then they need to be adjusted by a trained mechanic.
• Grab the seat by its nose and tail. Try to twist the seat back and forth, as well as up and down. If it moves, have it adjusted; if it makes noise, have it checked out!
• There is nothing quite so scary as to be riding and have your saddle break, leaving a sharp, nasty stem pointing at places it shouldn't be!
• Get on the bike, and apply the brakes, really, really hard. If the cables slip, snap or feel 'off', have them looked after by a mechanic.

Periodically:

• Inspect the tires. The rubber should feel like rubber, not hard or plastically. There shouldn't be any cracks or bulges. If any of these conditions exist, replace the tires immediately.
• Spin the tires to make sure that they travel free, easy, and noiselessly. There shouldn't be any grinding coming from the hubs (a regular clicking sound is normal for the rear hub), and if you tried to move the tire from side to side, there shouldn't be any play. The brakes shouldn't rub against them.
• Examine the crank arms (the things that the pedals attach to). See if there is any looseness, clicking or play in them.
• Straddle the bicycle. Then holding the handlebars, lift the front end gently off the ground, and turn the handlebars back and forth. Notice if there is any notchiness or grinding when you are trying to turn the bars.
• Lubricate (oil) the chain, and wipe off the excess. An old piece of terry-cloth toweling works great for wiping the excess oil and goop off the chain.
• Lubricate the cables.