Just finished it, 8/8. I mostly approached it by winging it and shuffling things around that looked good and like it was approaching the goal, since there's plenty of time to finish.

I still don't quite understand the exact mirroring rules at play.

I got stuck on 7/8 for a good while because I learned the rules wrong. I thought every bracket square needed to be lit.

You control the mirroring by moving the axis, they're what reflects your shapes. So my first move was always to identify the symmetries in the target shape, and position the axis accordingly.