Influence, affect & effect

We say something/someone has a / is a good/bad/positive or negative influence on someone/something:

John's new friends are a really bad influence on him.

Influence can be a verb or a noun:

verb: The media influences the way many people think.
noun: The media has a major influence on the way many people think.

Remember that effect is a noun and affect is a verb. These can be used in a similar way to influence:

verb: The media affects the way many people think.
noun: The media has a major effect on the way many people think.