how do you add movement to lens flare

are you using AE's lens flare effect? you have a flare center position that you can animate and this will move your lens flare.

if you want it behind the text layer just create a black solid layer and apply the lens flare effect to the solid.

if this isn't working for you then you should provide more information about what exactly is your setup and what you want to accomplish. a screenshot can help too.