Organization can come in many forms and at many levels. You can organize your images at the drive level (by using a system of folders, subfolders, and file naming conventions) and/or at the metadata level in Lightroom. You must first decide what organizational workflow fits for you. There are many websites and books devoted to this topic. You should do a little research before embarking on this adventure.
The best website I can recommend to you to delve deeply into industry standard organization practice is dpBestFlow.org from the American Society of Media Photographers and funded by the Library of Congress. The site is full of suggestions and videos. Get ready to spend some time there!
Lightroom has the tools but you need to plan. Start by deciding how you want to organize your images. I suggest you have one master folder into which all other folders and files will go. Doing so gives you an advantage when you decide to move the collection to a larger drive. Lightroom can relocated things better when they are in a logical folder structure like this.
There are four key components to any organization plan in Lightroom: folder/file naming, metadata, keywords, and collections. And, it all starts at import!
When you bring up the import dialog there are several sections that allow you to start organizing from the start. The first is the File Handling section.
A quick note about this feature - currently Lightroom will not apply any file name changes you set up to the backed up files. However, this has been addressed in Lightroom 3 Beta. Any file name changes you make during import will be applied to the backup files as well. That will make it much easier to locate a file for a renamed image.
So, whatever folder structure scheme you have adopted can be implemented in the import dialog.
The next section is File Naming. Here you can apply the file naming convention you have adopted.
In the Information to Apply section, the two critical organizational fields are Metadata and Keywords. You should have at least one metadata template set up with all your contact information, copyright, and rights usage data. Choose this from the drop-down or create one now. In the Keywords field enter all the keywords that apply to the entire set of images you are importing. (You can add additional keywords to individual images later on.)
Now when you import the images they will be placed into your folder structure as planned already tagged with essential keywords and critical metadata will already be applied. Adopting this discipline will give you a large head start on organizing your images!
Now, within the Library module we can continue our organizational magic with collections. On the left panel you will find the Collections section.
Collections are virtual groups of images that you bring together for some purpose. You can use this feature to further organize your images. There are two types of collections: regular and smart. With a regular collection you deliberately include images by dragging them into the collection. These are more static. Smart collections, however, are based on rules you set up. So they are more fluid and automatic.
For example, if we shoot regularly for ABC Corp we may want a collection of all the images we've taken for that client. From the example above we tagged the images on import with the keyword ABC Corp. Knowing that we can create a Smart Collection to gather all these images into one place.
Start by clicking the + next to Collections and choosing Create Smart Collection... from the contextual menu.
Give your Smart Collection a name in the Name field. In the rules list choose Keywords as your field, contains all as your operation, and then enter ABC Corp as the keyword you are looking for. Click Create and a new smart collection will appear under Collections.
Collections are a deep and powerful feature in Lightroom and we have only barely scratched the surface here. Play with them and discover how rich they are.
Whatever organizational plan you adopt one of the most important things you can do to make it work is to be consistent! You can always reevaluate your plan. Until you do be strict and stick with the plan you have. If the plan makes sense to you then you will be able to locate any image very quickly and that is the real benefit to being organized.