www.alphadictionary.com

When do you pick them? How do you know if they are ripe or perhaps over-ripe?

Here's a little piece from The Chronicle of Higher Education that addresses this question, a bit:

http://chronicle.com/blogs/linguafranca ... y-cliches/

What do you think? Should clichés always be eschewed, or welcomed at times?

It depends on so many things. Which cliché, and what is the context? As with any word or phrase, any author should pick the one that fits exactly. More likely, this would be a light piece, perhaps a comedy or a satire. But it's also possible that a cliché says exactly what you want to say in a serious work. After all, it became a cliché because it was a useful expression.