I went to a build night at Leicester Hackspace where we made Christmas cards using Chibitronics. Not something I've used before but they are little stickers with electronic components on, we connected them up using sticky back copper tape, super easy and good fun.
I made a penguin with lights that fade in and out in sequence.
Step 1: Design
First I sketched out the design on some card with a tab in the lower right for the battery. If making it into a card then including the back of the card at this stage would be easier (rather than doing it at the edge as I did).
I then designed the circuit, using cut out templates of the chibitronics stickers (there's a template here) and different coloured pencils to design the circuit (allows you to easily see which wire is positive and which negative). In this circuit they go through an effects sticker to fade the LED lights in and out. There are several videos and guides on the chibitronics website teaching you how to design the circuit which is worth a look.
There are two battery templates to see where the battery terminal would end up once the flap is folded to complete the circuit.
Step 2: Making the circuit
Having designed the circuit I started sticking it down, first the copper tape making sure not to break the tape - all corners are folded (this is important, some people did break the tape and the resulting connection was poor*, so keep it as one piece as far as possible). The LED and effects stickers went on top.
I made a hole where the battery was to go and poked the wire through to allow it to be mounted on the back of the card.
Once the battery is stuck to one side (ours came sticky, but you can use a few drops of super glue), simply fold the flap to complete the circuit and hurray! It works!
*If you do break it some people did solder the connection and it was fine, I did have one break because my tape wasn't long enough and taped about an inch over the top of the other bit of tape, probably overkill but I had no connection problems doing it this way.
Step 3: Making the card
I made the front on a bit of paper slightly larger than the card to allow me to wrap it around the card.
I assembled it by cutting out and sticking down bits of card, tissue paper and googly eyes, wrapped the edge around the card and taped it down, taking care that the copper tape wasn't covered where it needed to connect the battery.
Not photographed is me loosely taping down the flap to contain the battery, without enough force to make the connection but as the battery fell off once I wanted to make it a bit more secure and tidy it up a bit. You squeeze the corner to make the connection and activate the lights.
To make into a card I used double sided tape to attach the whole thing to a blank card. A more sensible approach would be to have included the other half of the card when starting out in step one.