Install a brand new plug. (Put the old plug in your pocket and bring a spark plug wrench.)
Warm up the bike a little.
Find a safe stretch of road about a mile long.
Bring the bike up to speed and maintain a _steady speed_ for about half a mile.
Kill the engine at that speed and coast to stop. Do not slow to a stop with the engine running or the plug-test is meaningless.
Pull the new plug out and reinsert your old spark plug and drive home.
Examine the new plug under a powerful magnifier..
If done carefully and the plug's condition is interpreted correctly, you will get a snapshot picture of engine conditions at the particular speed you chose.
Always use a new plug everytime. Photos of plugs and what the different insulator colors mean and what the different conditions of the electrodes mean are easily found on the net..
If you need more info, just ask.