C is true of A.
	B is similar to A.
	C is true of B.

Examples:

It is true of rats that nicotine causes cancer in them.
Human beings are similar to rats.
So, probably, nicotine causes cancer in human beings.

Jane loved it when I sent her roses.
Sally is similar to Jane.
Therefore, Sally will love it when I send her roses.

Arguments by analogy are non-deductive. They are not "valid:" the premises might be true while the conclusion is false. But they can be strong or weak.

How strong an argument by analogy is depends in large part on how similar the two things are.