Attending a J-league match
1. Since most visitors don't have a favorite team, pick a match with date/time and venue that work for you. Some venues are notoriously difficult to get to, like where Zelvia Machida plays. Watching a J2 match isn't bad either. There's not too much dropoff in the experience and entertainment factor between J1 and J2 imo. A somewhat important factor is the size of the stadium and whether it is football-only (as opposed to having track separating the field from the seats).
2. Buy ticket in advance using the ticket booking machine at a convenience store (eg, Family Mart, Lawson, etc). Whether/not this is possible in English has been discussed elsewhere but I'm not sure what the conclusion was (I'm Jpnese... someone help). You select your preferred seat zone, but choose carefully and I would avoid the area behind the goal where there tend to be fanatics.
3. On the match day, I'd arrive at the stadium at least 45min before kickoff. There're various stalls, atmosphere to be taken in, and you get to watch players warm up up-close.