Step 1: Get a Pantload of Soda Tabs
The other part is to get more than you need. Really. It always takes more tabs than you think, and nothing is more frustrating than trying to finish a piece when yiou have run out of tabs! You might find yourself wandering the streets, looking for the errant aluminium can, hoping... hoping...
Step 2: Get Coloured Tabs
More and more beverages are going to a coloured tab, particularly energy drinks. A large portion of mine come from Rockstar and Redbull cans. But be careful with these tabs as well... Usually one of the two "windows" in the tab is unpunched, leaving it for you to CAREFULLY remove the "pane" with snips or other metal removal tools of your choice before use in your inlay. This is sometimes the only way you can get a particular colour into the weave.
Step 3: Lay Out Your Image on Paper
Find the image you wish to inlay. The more simple, the better. This is not to say that you can't use a cool pic that you found somewhere, it just means that it needs to be made more "simple"... Think about how a pixellated image gets the idea across without all of the detail. That is what you are wanting to go for for inlay on a piece that will be used as a costume. Much larger pieces can be done with lots more detail, but for the scope of this exercise, we are doing the minimal detail. Hence a cross in my demonstrated inlay. It could only be simpler if I did a straight line.
Make (or purchase) a piece of graph paper with a 1" grid.You can also find graphing paper online that can be printed to any size. I would recommend the paper be no smaller than 12X12" (if possible). I've taped multiple pieces together (lining up the grid) to make it as large as I need. Then "fill" the grid in with your design. Each square represents a single tab. So filling in the squares with your design colors, this gives you a good idea of what it will look like once assembled. This is much like making a cross stitch pattern, though a great deal larger. This lets you know what colours go where.
Instead of actually colouring in the squares (which is just fine if you like), I like to just place the actual tabs that I am going to use on the paper. Then, as I construct it, I can just remove each tab from the paper as it goes into the final piece. If you are going to make more than one piece with this particular motif, I would recommend doing the coloured in squares on the grid, so you can accurately make the image more than once.
Step 4: Make a "starter" Piece of Soda Tab Maille, Then Add On
It is easiest if you add the inlay tabs one row at a time. That way, you will be able to keep it all straight. And should you need to put it down and come back to it later, you will know right where you left off, and where to start up again (Which will minimise swearing and aggravation).
Depending on your method of constructing the soda tab maille, you may have some distortion in your image when it is used in the final piece. But hey, that's what experimentation is for, right?