This is an advanced theory resource, for students studying Grade 6 music theory and above, and for students of A-level music.  

Remember that a 6/4 chord is a second inversion chord.  You may only use second inversion chords at recognised places, such as in Cadential 6/4, Passing 6/4 and Auxiliary 6/4 progressions.  You will need to learn these thoroughly, and then be able to apply them to any key.