Listen to rhythms you hear during your daily routine. Mimic those rhythms by clapping your hands quietly or loudly. When you find rhythms you like, record them into your portable audio recorder.
Speak various lines of text, which could be random words, syllables or full sentences. Speak or sing combinations of all three of the aforementioned concepts. Speak or sing them at various speeds from painstakingly slow to as fast as you can clearly get the words out. Record the variations you like into your portable audio recorder.
Listen to various genres of music in your music collection and write down the titles of the songs whose rhythms you like. Using musical notation, symbols, words or numbers, notate rhythms that you'd like to use for your song from the tracks you listened to.
Open up Garageband or a similar recording program on your computer and listen to the rhythmic samples and loops that come with the program. Listen to the differences between the rhythms of the individual instrument samples and the rhythms of the various grooves. Drag and drop the rhythms you like into the Garageband window to save for when you are ready to create your song.
Turn on your drum machine and sample the various rhythms that you can make by pushing the pads, turning the dials and working with the metronome built into the machine. You can also check out the preprogrammed rhythms the machine comes with and pick from those as well.