You can install a micro SD card and move a few apps to SD if possible. If that's not enough, root your phone, partition your sd card so it has an ext4 partition and install Link2SD from Google Play. Then, you can move any apps to your sd card.
Current device: Oneplus One 64 GB Sandstone Black
No support via PM! Please ask in a public thread, I'll help you as much as I can.