I'm struggling to fully conceptualise "metaphor". I think I understand "simile", it is an explicit analogy. But how can one turn any analogy into a metaphor?

So:

1. Is there anything to bear in mind about turning an analogy into a metaphor, bar grammatical code like making sure it's a complete sentence?
2. Is there any surefire way to turn an analogy into a metaphor proper? E.g.: a colon, to signal that I am explaining the tenor; or simply writing a simile then omitting the explicit comparison.

In my example for 2

• I stay quiet like a broken fire alarm.
• I stay quiet: a broken fire alarm.
• I stay quiet, a broken fire alarm.

I'm struggling to fully conceptualise "metaphor". I think I understand "simile", it is an explicit analogue. But how can one turn any analogue into a metaphor?

So:

1. Is there anything to bear in mind about turning an analogy into a metaphor, bar grammatical code like making sure it's a complete sentence?
2. Is there any surefire way to turn an analogy into a metaphor proper? E.g.: a colon, to signal that I am explaining the tenor; or simply writing a simile then omitting the explicit comparison.

In my example for 2

• I stay quiet like a broken fire alarm.
• I stay quiet: a broken fire alarm.
• I stay quiet, a broken fire alarm.