I've always had a tendency to over season, so I really try to watch it. Really what it comes down to is personal taste and perception. What one calls a light rub another may see as over rubbed. With trial and error you'll eventually find what is just right for you.
There is a lot of great advice here, but Mahoney86 is spot on. Keeping an acurate record of your cooks can be a real PITA sometimes, but when you find the process that really hits your hot button, it does pay off. I hate it when I cook something on the fly that comes out just spectacular, but I can't replicate it, cuz I didn't really pay careful attention to what I did.
Weber Performer with rotisserie ring, 22.5OTS, Maverick 732, Weber Smokey Joe,PBC Smokenator/Hoovergrill, variety of microbrews, Gin and tonic, variety of lighters.