This is a great technique for doing multiple-exposures. First of all, I shot a roll of film through my SLR using a custom bokeh mask. The basic idea behind the mask is that it changes the out-of-focus areas from standard circle-ish shapes to fancy shapes such as stars, faces, hearts etc.
It works particularly well in dark situations with lots of lights in the background. Here is a great tutorial on how to create your own custom masks
I shot my roll around town one night – streetlights, traffic lights, etc. I used a large aperture (f/1.8) and made sure the lights were out of focus – this led to maximum custom shapes. You don’t have to go round town to shoot lights – you could just put some fairy lights up in a dark room (I used this option for my second attempt – it’s much warmer and quicker!).
Once I finished the film in my SLR, I put it into my trusty Lomo LC-A and shot normally. I think I got some rather pleasing results. The cow with a star in her mouth and the silver planetarium are particular favourites…