Do twoja kieszeni odkładaj koki!
Rybnik is almost right and Yaskier is 99% right.
But I am going to tell you why your version was wrong.
The sentence is in imperative, so it should start with a verb. Your reordering was unusual to say the least; location in Polish is usually put at the end of a sentence, as in "Idę do szkoły", and not "Do szkoły idę". There is nothing particularly wrong with the latter though, as Polish is flexible in this respect - as Latin is. So the first correction would lead to:
"Odkladaj koki do twoja kieszenia"
The next big change: You would normally use the perfective form of a verb if your 'command' stresses the completion of the action, and the imperfective form if the command stresses the actual activity. So here you should use perfective "odłóż" (from odłożyć) rather than imperfective "odkładaj" (from odkładać):
"Odłóż koki do twoja kieszenia".
The noun "koka" should be used here in accusative case "kokę", rather than genetive "koki".
"Odłóż kokę do twoja kieszenia".
The noun "kieszeń" has a feminine form; the locative case is therefore "kieszeni" (not masculine "kieszenia"). Similarly the pronoun "twój" should agree with "kieszeń" declension-wise - "twojej kieszeni", not "twoja kieszenia":
"Odłóż kokę do twojej kieszeni".
One more tiny correction: it is better to use "swój" rather than "twój" here. See the thread
Use of swoj.
"Odłóż kokę do swojej kieszeni".
Now we get a grammatically correct sentence, but still not quite perfect.
The pronoun "swojej" is redundant here, as there is clear from the context whose pocket we have in mind.
"Odłóż kokę do kieszeni".
The verb "odłożyć" implicates putting something aside rather than inside. "Odłóż to na chwilę (na potem)"; "odłóż to na bok". The correct version of this verb here is "włóż".
"Włóż kokę do kieszeni".
Finally, Rybnik and Yaskier correctly used another verb "schowaj" (rather than "włóż), which means "to hide".
"Schowaj kokę do kieszeni".
You could emphasize this sentence a bit, depending on your intent.
"Schowaj tę swoją kokę do kieszeni" - in a sense "go away, I do not need it, I do not want anything to do with it"