I have been a fan of these teams since I was about 4 years old: Lakers, Clippers, Dodgers, Angels, USC, UCLA. Formerly Raiders and Rams as well, but they both left L.A., so forget them! My loyalty is to the city of L.A. and the surrounding areas, not necessarily to teams who choose to leave. But, where I'm going with this is that I don't really have time to watch every single game. Because of work, I sometimes go long stretches where I can't watch my team(s) play. If I had time, I'd watch every single game. But, I don't so I have to just read the box score each morning on Yahoo Sports or espn.com to see if they won/lost and how the game unfolded. So, at any given time, I know what's happening with my teams - what place they are in, who is hurt, the fact that they haven't been playing up to their potential, etc. I keep up with them as I'm able to. Let's say I keep up with one of my teams "haphazardly" during the year, but then the playoffs start - and I get really interested. That can be seen as bandwagon behavior, but to me it's not because I've kept up with them all year, I just didn't have time to watch every single game on TV and sit on the couch with my foam finger cheering them on.
To avoid being a bandwagoner, do the following:
-know what's going on with your team. If you can't watch the game, then take 5 minutes the next morning and read the box score/summary in the paper or online. Watch those weekly 30 minute segments on cable TV like "Detroit Lions Insider" to see interviews, hear the coach talk, etc.
-I have a friend who says, "I LOVE the 49ers" and "I have to have my football. Without football, life just isn't the same." But, this person knows virtually nothing about the current team and says stuff like, "We have a big rivalry with the Chiefs and we always beat them." Um, no, I'm sorry to break it to you, but the 49ers and Chiefs do not have a rivalry. When the 49ers were 0-4 this year, this person argued with me that the 49ers had already won a game. Basically, if you don't know what you're talking about, don't act like you do.
-if you know "nothing" about the team all year and then you're super excited during the playoffs (like OMG, I hope they win soooo bad), you've officially "jumped on the bandwagon".
-know how the game works. Know the difference between a kickoff and a punt. Know what a screen play is. Know the difference between a pass interference call in college football vs. a pass interference call in the pro game. Know the difference between the overtime rules. Know all the positions on the field, etc. At least the basics. And that just comes by watching a few games and listening to the announcers. If you're at a noisy bar, you'll never learn what's really going on - the intracacies of the game.
Basically, just continue to gain knowledge about your team as time goes on and you'll become a fairly knowledgeable fan. You'll be able to read an article and know what is being said and you'll be able to talk to other sports fans and have some good insight into what is going on with the team. Know the team and what is going on; don't just show up during the playoffs and say, "Hey guys, isn't this exciting!?" Cuz yeah, it's exciting, but it was exciting for the past 5 months too.