Another way to come up with fresh ideas is to analyze genres of music that you do not write in. If you write pop tunes, spend some time with classical, jazz, blues, reggae or old R&B stuff. You will discover things that you'd never hear if you only listened to pop songs. Be open to all styles and use them.
Back in the 1940's, writers would take the entire chord progression of an existing tune and put a different melody on top of it. Why not give it a try? Be sure to come up with your own melody though. You don't want to get involved in copyright infringement.
Here's a little list of things I do to trick myself into coming up with something different:
~Play in a key that you are not familiar with.
~Write on an instrument that you don't play.
~If you play guitar, limit yourself to three strings.
~If you play keyboards, limit yourself to only one hand.
~Write a tune using only the bass line. Fill in chords and melody later.
~Learn a new chord and write a song including that chord.
~Write a song. Now keep the melody and use different chords.
~Write a song. Now keep the melody and use chords in the relative major key. (If your song is in C minor, re-harmonize the tune in Eb major.)
~Do the same thing going from major to it's relative minor. (If your song is in C major, re-harmonize the tune in A minor.)
~Write a tune by starting with a drum pattern.
~Write a tune using only one chord. Two chords. Three chords, etc.
~Write a tune with all major chords. Minor chords. Augmented chords, etc.
~Write a progression. Now play it backwards and make a song out of it. Do the same thing with a melody.
~Close your eyes. Now drop your hands on a keyboard. Remember the first four chords that come out. Force yourself to write something using only those chords.
I'm sure you could add many more tricks to the list. The point of the exercise is to get away from the devices you are comfortable with. These tips are especially useful if you are experiencing the dreaded writer's block. Now, if we could only come up with a way to get more time to write!
Have fun, don't be afraid of your first thought, never give up!