Get familiar with music notation. Music is written on a staff that features five lines and four spaces. There is a music staff for both treble and bass clef. For the piano, these staffs are put together to create what is called the grand staff, so named because it features bass and treble notes. The notes on the treble clef are F, A, C and E for the spaces. The lines are E, G, B, D and F. The bass clef spaces are A, C, E and G. The lines are G, B, D, F and A. It's a good idea to keep a note chart next to your piano that shows you where the notes on your keyboard are located. You can purchase one of these charts at a music store or use one of the many online free of charge. Eventually you won't need this chart, but until you get used to the notes, it doesn't hurt to refer to one.
Focus on learning as many chords as you can. You can buy a piano chord book at a music or book store. You can also find extensive piano chord dictionaries online at no charge. The more chords you know on your piano, the more songs you will be able to play quickly. Piano players often use sheet music arrangements called fake books. A fake book is typically a large collection of popular songs with nothing more than chord symbols, a melody line and lyrics. Combining a fake book with a library of memorized chords allows you to open a fake book and play a variety of simple arrangements. Make a habit of learning two or three chords a week on your piano and you will notice an immediate improvement in the number of songs you can play and sing along with.
Purchase a book of easy piano songs from a music store or visit one of the many Internet sites that offer free easy piano music. The best way to become a better player is to start with easy piano classics everyone is familiar with. These songs may include "Oh Susannah," "Fur Elise," or Bach's "Minuet." Playing simple arrangements of these songs will get you accustomed to the keyboard, and as you improve, you can step up to intermediate and advanced versions of the same music sheets.