Step 2: Make a Pattern
Use an image search to find a star chart that includes your choice of constellations (or use my pattern.) You could, obviously, just make one up as well. Import that image into Illustrator or some other draw program. For this size mold you need to adjust it to fit within a 2.5 inch by 5.5 inch space. You'll need a bit of margin around the outside edges. Draw a little circle for each star you want to include. Draw about a 1" circle for the battery pack and another .75 inch or so circle for the switch. You'll place these in a few minutes.
You need to draw one line on one side of the stars for the positive wire, and a line on the other side for the negative. These lines can NEVER touch. If you're experienced in electronics you can probably skip over the next paragraph, if not read on.
The positive line will need to touch the positive side of each LED, will need the resistor added to it, will need the switch added to it, and will need to end on the positive terminal of the battery holder. The negative will need to touch the negative side of every LED, then go directly to the negative terminal of the battery holder. This information is important when placing the switch and batteries.
Adjust the constellation in the 2.5 by 5.5 inch space until the end of the wires can connect to the resistor, switch and battery pack without touching each other. This might take some crafty planning and adjusting. I've included a wiring diagram of mine for reference. Be sure to orient the battery holder so that you can easily change the batteries (if the open side of the holder is next to the wall you'll have to do a lot of prying to change your batteries.)
Draw a 3 by 6 inch rectangle around all of it, group it and flip it. It needs to be reversed because you build the light from the front to the back, so you're looking at the back of it while you're working. I printed mine twice on the sheet so I had one to place beneath my mold and one for clear reference, taking notes on, etc.