Good military operation names are picked for these reasons: to deliberately deceive the enemy, to have no association with the operation whatsoever, to raise the morale of the troops, or for political/marketing reasons.
The US is big on giving high level operations that will be announced to the public impressive names like "Desert Shield", "Desert Storm", "Desert Sabre" and "Just Cause". These are operations that are already intended to be discussed in public. The names are picked so the press isn't talking about "Operation Blue Spoon" (the original name for Just Cause). They usually contain many, many lower level operations with more secure names.
Operation Vittles was the name for the US airlift of supplies to West Berlin during the blockade. Operation REFORGER is an acronym for "REturn of Forces to GERmany" and it's also symbolic of the intention to reforge the German army in the event of a Soviet attack. Operation Magic Carpet returned US troops to the US after WWII. Operation Eagle Claw would have had US special forces snatch US hostages out of Iran using helicopters (it was a disaster). And so on.
The British military, more secretive and devious than most, called their operations in the Gulf War Operation Granby which is the name of a British commander in the Seven Years War and has nothing to do with Iraq. Again in 2003, what the US called Operation Iraqi Freedom the British called Operation Telic, and the Australians called Operation Falconer. During WWII Prime Minster Churchill would regularly tinker with operation names (and everything else) he thought might give something away.
If you look at the list of Japanese operations, they give a lot away in their operations. Operation AL is an attack on Alaska and Aleutian Islands, Operation MO is on Port Moresby, Operation MI is on Midway, etc. These names were likely picked for expediency during early planning and never changed.
The invasion of Normandy was originally Operation Slegehammer. The lesser known invasion of southern France was Operation Anvil to match. They were changed to Overlord and Dragoon to avoid any information leaking out. (D-Day was Operation Neptune).
Going the deception route, the German invasion of Denmark and Norway, very much intended as a surprise, was called Unternehmen Weserübung or Operation Weser Exercise implying an exercise on the Weser river nowhere near Norway. As this was during the Phoney War or Sitzkreig period, the "exercise" part fed into the Allied perception that the Germans weren't going to attack. Later, Germany would do the same thing with Unternehmen Wacht am Rhein or Operation Watch on the Rhine implying a plan to defend the Rhine River which is exactly what the Allies expected; this was the code name for The Battle Of The Bulge.
If you want to know more, this article from Parameters goes into some detail about military naming choices. You can also pick through this list of military operations and find plenty of examples, though keep in mind that list is likely to contain more high level and popular operations which are more likely to be political branding.