Using Masks
Before-

After-

1. Open up your image. You can see mine in the before picture.
Credit
2. Create a new layer. Make sure your foreground color is black. Take any brush (I used 50px round brush) and scribble all over the image.

3. Move the scribble layer under the image.
4. Hover your mouse between the two layers (dotted line in the screenshot). Hold the
alt key. When your mouse turns into a 2 circle thing click on it.

And that's it. You should have a result similar to mine.
If you're using a premade mask, just paste the mask instead of scribbling.