Coming up with synth lines

[Purpleb]

I usually come up with a melody and some chords, then I create a bass pattern and a drum pattern. then usually add a pad or riff. but a lot of time I feel the song needs to have more drive in it. The music i make is electronicish with vocals. I am thinking maybe a syncopated synth line should add that push to it.
I was wondering how do you come up with synth lines?? or syncopated lines in general?? any tips would be apprecaited

 

[dementedchord]

mirror the melody or bass... that is to say double it... or parallel movement... or echo it...

contrast it... wher the melody moves up move down...

counterpoint... think of this as a secondary melody... try writting another melody that could stand on it's own but sounds good played over the top of the original melody...