You can build up word banks like this one.
Snake
Slithers
Slides
Slowly
Scaly
Smooth
Scary
Silent
Soft
Then you could try and make up a snake poem using 'S' throughout
to show alliteration.
The snake slips and slides
Slowly, smoothly.
It scales slither
Over soft grass,
Snaking silently to
Scare its prey.