Rev's comment below that Avengers # 300 was his first issue got me thinking: How did Marvel snag us, and get us to buy more of its interconnected universe?
For me, it started with Iron Man # 225. Perfect starting point, the first chapter of Armor Wars. From there, I moved on to WCA, since he was a member of the team. I got there just in time for # 37, which split the team up as Hawkeye & Mockingbird fought over the right to let a villain die.
About a year later, for my 13th birthday, I got a gift certificate to the local paperback store ... and went nuts. I bought Daredevil # 262 (part of Inferno), Cap # 349 (the penultimate chapter of John Walker as Cap!), and ... oops, Rev, it may have been Avengers # 299, as part of Inferno.
But I guess what really got me was Uncanny X-Men # 241. At 13, there was nothing to draw me in better than Maddie Pryor, spread eagle in her mini Goblin Queen outfit. I read that issue over and over, and picked up every issue since.
So what's your story? How did the Marvel marketing team get you to branch out and buy not just your first comic, but begin to sample their other titles?
It is entirely possible I had a comic or two before this, but at some point around 1990 there were Marvel figures with an offer for a free year's subscription on the back of the box. My parents agreed to let me send away for two and soon I was reading Captain America and the Amazing Spider-Man every month. It was pretty sweet. Landing in the Gruenwald era of Cap (around the 390s) I really found myself enjoying the books. I also liked whatever Spider-Man story was running around the same time, but Cap's book just grabbed me more.
Another thing that helped draw me in were the Marvel Universe trading cards they had in those days. Trying to hunt down the full sets I learned about all sorts of characters I probably wouldn't have had time to learn about with just a few comics a month. (Later on I found a Marvel Handbook at the local library and checked that out more than once as well)