Bicycle checklist

Handlebars should be square with the frame and level with the saddle. Movement should be neither too stiff nor too loose.
When on the saddle, both feet should just touch the ground.
Your wheels should be straight and in line. Replace wheels if they are buckled or out of alignment.
Tighten loose spokes and replace any that are damaged.
Make sure your tyres are properly inflated, with a good tread.
Make sure mudguards are secure and well clear of the wheels.
Check your gears and get them adjusted when necessary.
Check your brake cables and adjust them when necessary. Replace them when frayed.
Make sure the closed ends of brake shoes face the front.
Make sure brake blocks are close to the rim of the wheel. Replace worn blocks.
Check pedals and replace them when worn or broken.
Make sure your lamps are white or yellow to the front and red at the back. Use a red reflector. Replace batteries when necessary and clean lenses.
Make sure your bell is within easy reach of your thumb.
Oil all moving parts.
Wear a cycle helmet at all times.

A bicycle should have the following braking system:

If it has one fixed wheel or is designed for a child under 7 years of age, it should have at least one brake;
If it is designed for an older child or an adult or neither wheel is fixed, it should have one brake acting on the front wheel and another for the back wheel.