Well, this thread hasn't gotten much attention in a week, so I'll chip in my 2 cents. (I've already steeled myself against being early for Groundhog Day or other rodentia-themed humor

)
First, I'll echo Oracle's comments about working any game I could. It seems like I worked kids' games every single weekend for about my first 4 years (starting in '92), even after I started getting some JV high school games. I worked a lot, and it helped me see a lot of plays. Part of officiating is simply having seen it before and not being surprised by it, so that when it happens the next time, you know how to handle it. Working so much those first few years showed me a LOT of plays to store up for later.
And I always tried to work those games "the right way". I switched after fouls, I took POEs seriously, I tried to hone my mechanics. Many times, I see guys going through the motions in 5th/6th grade games. I worked my kids' games as though they were Varsity games.
Second, I sought and soaked up as much constructive criticism as I could get. I asked nearly every official I worked with, every Varsity official who followed my JV games, "Did you see anything I can work on?" Sometimes, it was not very helpful; but once in a while, I got something significant that I could try to improve.
Third, I studied the rules and mechanics manual. A lot of that happened here and at McGriff's. But I also tried to ask my interpreter questions after meetings (without monopolizing his time); and I studied the casebook quite a bit.
All of that got me to the HS Varsity level in my 6th season ('97). To get into D3 NCAA ball, I filled out an application and was accepted to my local association. I worked at the Associate level (JV and Juco) for 3 seasons ('98 - '00). After each of the first two seasons, I fully expected to be moved up to Varsity, and was extremely disappointed when other officials were promoted and I was not. After that second season, I almost gave up and returned strictly to a HS schedule. I decided to stop obsessing, work as hard as I could on my 6 JV games and not worry about what I couldn't control. After my 3rd season on the Associate list, I was promoted to the Varsity list for the '01 season.
To get to the next level, I have only one word for you: CAMP.
The key to Division 1 officiating right now is camps. For better or worse, I am a product of officiating camps. D1 assignors do not have the time to go around to hundreds of high schools and D3 colleges to look for talent. You have to go to them. You do this at camp.
Yes, it's expensive. My least expensive camp was $325 and my most expensive one was $550, plus airfare to Florida. (I have heard that the Big East camp is by invitation only and is free, but I don't know that firsthand.) Yes, it's time-consuming. Most camps run at least 4 days, and that's not counting the travel to get there. And NO, attending these camps -- even 3 or 4 or 5 times -- does not guarantee that you will be selected to work a D1 conference.
But I worked at camp with the same attitude that I had in those early years -- work every game hard, the right way; and I soaked up as much instruction as I could.
I was hired by my first conference for the '06-'07 season, and my second conference the next year. I had some surgery this summer, so I was unable to attend the Colonial camp or the America East tryout. I was bummed about that, but it was necessary. I work a very modest schedule of D1 games (10 games), but I am frankly ecstatic that I have them at all.
Oracle is also correct about the time commitment. College ball, in general, requires a bigger time commitment than HS. We're required to be at the game site 90 minutes before tip. But at the D1 level, the travel is also a LOT more. Not so much for me personally (my longest trip this year is 3 hours), but for guys who make it to the big conferences, their travel includes flights and hotels and can require long stretches away from the family.
I hope that's interesting to somebody.