There are many ways to prevent rusting of Iron:

Galvanization

Galvanization is a process in which the Iron sheets are coated with a layer of Zinc which prevents rusting. Zinc gets oxidized more readily than Iron. So, the Iron remains protected.

Painting

Painting the Iron surface will create a barrier between the Iron and the atmosphere, which will protect the Iron from rusting.

Electroplating

Iron sheets can be electroplated with a metal which is more reactive than Iron, so that instead of the Iron getting oxidized, the other metal gets oxidized (because it is more reactive).

Bluing

Bluing is a useful technique which offers limited protection against rust for small steel items. The term “bluing” comes from the blue-black appearance of the finish when using this technique. Blueing is often used in firearms manufacture to provide a degree of corrosion resistance. It’s also used in fine clocks and other metal work.

Bluing is accomplished by immersing the steel parts into a solution of potassium nitrate, sodium hydroxide and water.