There are many ways to file images and many software programs to help you, however I think it is best to make up your own hierarchical folders using a range of topics that suit your photography and lifestyle.
If you use one particular software to organise your photos it can be very hard to extract your photos from that software system at a later date. Picasa is a popular editing / filing system however it tends to take over your computer and over sort your photos in ways that make it difficult to find them. I recommend you take Picasa off your system, make your own image folders and use Photoshop Elements for editing.