Mixing up the chords to modulate in a tune.

How to make a song more interesting?

In the words of one of the best songwriters of all time proven by his track record (Barry Manilow), you must not make the song predictable.

For example, if you know that the chords that a major key (and its relative minor) calls for are in this order:  major, minor, minor, major, major, minor, half diminished (I - ii - iii - IV - V - vi - vii half dim.), then mix this sequence up a bit.  How?  Borrow!!!

Make any of the minors, majors!  For example try in the key of C major making D a major triad chord instead and then always resolve the transformed chord by playing up a P4 (perfect 4th) back in key…so the D major chord in the key of C major would have gotten resolved by a G chord in the key of C major.

What did you do?  You added spice to your songwriting!!!