The shortest way is by adding the ObsoleteAttribute as an attribute to the method. Make sure to include an appropriate explanation:

[Obsolete("Method1 is deprecated, please use Method2 instead.")]
public void Method1()
{ … }

You can also cause the compilation to fail, treating the usage of the method as an error instead of warning , if the method is called from somewhere in code like this:

[Obsolete("Method1 is deprecated, please use Method2 instead.", true)]