When I first started taking photographs, I would just dump the photos onto my computer (an old dell desktop at the time), delete any that I didn't like, and edit the other using ms paint. no joke. I could actually take out blemishes using copy/paste in ms paint.
Years later I've finally come up with a work flow that keeps me sane and a saving/backing up system that keeps my work safe. Right now I'm going to go over how I keep my photos organized so I can easily find them.
First step - open up Lightroom and download my photos to my computer using their "import" function. I have it set up so that when I download my memory card to my laptop, it's saving not just on my laptops hard drive but also backing up simultaneously on my external hard drive (a Free Agent 250gb drive). I used to just dump everything into folders and not really organize... BIG mistake. Now I have it set up into trees. For example, if I'm looking for a photo that I shot a guy named ben back in January to email to someone, I open:
Photography > Fashion > 2009 1.8 Ben > watermarked and webready
and there they are! My photos are organized by type (Nature, Art Portraits, Commercial, Events, Fashion, Glamour and Nudes, and Headshots) then further broken down by the date along with the subject name or a brief descriptor. Inside each of those is a folder for RAW files, a folder for photoshop files, another for high resolution jpegs and a final one for webready images. I keep the original numbers attached to all the files so that they are easily referenced. So if for instance I upload the photo of Ben to dA, and someone makes a suggestion on ways to improve the retouching, I can easily consult the webready folder to figure out the file number. Then, knowing that it's file xyz2 I can go to my photoshop folder and look for file xyz2 to edit. This has saved me SO many headaches you can't even imagine!
What's great about Adobe Lightroom though is that it gives me even more power over how I file my images. When I import from my memory card to Lightroom I have the option to assign every photo a set of keywords. I have roughly 3000 photos cataloged on Lightroom, and a good chunk of those have keywords tagging them.
This means that if I decide I want to show someone all the concerts I've ever shot, I can type in "concerts" into the search field and every photo tagged with that word will appear.
I generally tag my photos with the date, name of the model, place it was shot (inside/outside, studio, location, a town or city name and sometimes the state if I feel like it, though that's not really necessary), and descriptors (female, blonde, blue eyes, tall, fair skin, black dress, high heels) and some words to pinpoint what kind of shoot it was - fashion, event, headshot, etc.
I also make sure to back up my work as I go. Every time I'm done with a project I back up the photos and other files onto my external drive.
Overall I've found that taking a few extra minutes to organize your photos and back them up in multiple places as you bring them onto your computer can save a lot of time and hassle later on, and I highly recommend everyone to come up with some system to keep track of their own - feel free to borrow mine :)