Posted By:
Al C.risafulliI started by buying everything under the sun.
Then I tried to narrow my focus by working on complete sets from every year the Yankees won the World Series. That worked really well for a while - it gave me 26 sets to build, all sorts of issues to choose from, at all different price levels. When budgets were tight, I could work on 1978. When budgets were a little more free, I could work on 1938.
Then I got frustrated that there were sets I liked, like 1957 Topps, for example, where I "couldn't" own a card. So I added a HOF type card set to my collection. Eventually, the coolness of that consumed me, and I got up to around 200 HOFers and 150 card types. Due to my fascination with this, I started liquidating the Yankee sets.
Then I started to realize that I'd like to own multiple cards of some HOFers, so I started adding to the breadth of the HOF collection. And suddenly I had five different Roger Bresnahan cards.
Then I started to realize that I didn't really want to spend money on Earl Weaver and Rollie Fingers, because I'd rather have "better" cards of older players. Eventually, I started buying nothing but prewar cards.
So I settled on the "Nifty Fifty," which is a concept I currently embrace. I also work on a few sets diligently - 1938 Goudey and W575-1 Henry Johnson Confectioners. Less diligently, I'm building off-grade T205 and T206 sets.
And to keep myself buying cards, I'm building a run of 1970s Topps baseball sets.
Lastly, I've recently started building a type set of the ABA All-Time team, and a type set of shiny autographed cards from the NBA's Top 50 players.
So you can see, I'm very focused. 
-Al