Some of idioms are: Left the 'straight and narrow'.
Became a prodigal. Wandered away. Chose the road most traveled.
Strayed away. Became a lost sheep. Started walking the byroads and byways.
Chose the highway to hell. Started slip-sliding away.
There are many idioms and phrases for 'on the back burner'. Some idioms and phrases for 'on the back burner' include 'pushing aside' and 'procrastinating'.
Astray means to go off the path or right direction. Synonyms include adrift, afield, amiss, awry, gone, lost, off, off course, off the mark, straying, wandering, and wrong.
One reason why some idioms are confusing because the way the sentences are worded
"Idioms for Being Afraid", "Idioms for Being Angry", "Idioms for Being Happy" are some examples of idioms found in the book "Found" by Margaret Peterson Haddix.
Here is a link to some idioms. You can pick the "non-common" ones for yourself -- some people have heard certain idioms a lot and others have not heard the same ones, so you'll need to decide that part.
Some websites that have idioms written in them include The Free Dictionary, Cambridge Dictionary, and Phrases.com. These sites provide definitions and examples of idioms to help users understand their meanings and usage in context.
savvy, brainy
"tearing down the park path" chapt 4 "nobody's going to hook me" chapt 4 "keep an eye on" chapt 4
The best place is to go on your search engine and type in "list idioms" You can also look at this question for some examples.
Nostalogic
cry unclemonkey's uncle