When I first got a DSLR I had one folder with every photo I ever took in it. I figured I would get to it later and, of course, never did. Months later, when I picked up Lightroom, I realized I had over 4,000 photos horribly organized. It would take me over 5 minutes to find one photo so I knew I had to come up with some kind of folder structure to organize my photos in.
After trying out a few different methods, I finally found one that works perfectly for me. The structure is very simple: I have one Lightroom catalog stored locally linking to an external drive where I store all my photos. Within my catalog I have one main folder called "Lightroom Catalog" with "YEAR" folders (2009, 2010, etc.) inside. In each "YEAR" folder I have every photo session organized as follows: "YEAR-MONTH-DAY SESSION." So if I were to take photos at Grand Central Station today my folder would be labeled: "2015-09-06 Grand Central Station"
What's great about this structure is that I typically remember the year and month of any photo session. Right away I can go to the year, look for the month, and now I only a small amount of sessions to go through. Ever since I moved my photos into this folder structure, finding photos has been a breeze, and the way the folders all line up looks beautiful. haha