Your bike needs regular lubrication to help it run smoothly and to reduce wear and tear on the components.
Your bike must be clean before you apply any lubrication. The most important item when it comes down to lubrication is your chain. If it feels dry to the touch or is starting to become noisy it's time for a lube using a suitable chain lube.
Other parts of the bike that will need a regular lube are brake pivot points, cables and derailleurs. Allow sometime for the lubricant to penetrate, moving the component will help, then remove any excess lubricant with a cloth. This will help to keep the bike clean.