When you use the Lens Flare filter (found under the Filter menu, under Render) it puts the flare in the center of your image, but you can actually choose the position for your flare center (which changes the look of your flare quite a bit) by just clicking-and-dragging the flare center within the filter’s Preview window. By the way, a great way to apply this filter is to add a new layer, fill it with black, then run the filter, change its layer blend mode to Screen, and it will blend in with your image, so you can drag it wherever you’d like (if an edge shows, add a layer mask and paint over the edges in black with a huge, soft-edged brush).
Excerpted from The Adobe Photoshop Book for Digital Photographers (2017 Release) by Scott Kelby.