A few things that I learned (and want to try to remember) from the recent penguin flock creation (here and here). I hope these will help others too. Some of these sound so obvious, it makes me wonder why it took me several softies before I decided to try them. And if you have any great tricks that you've come up with, please leave a note in the comments!
1. I enlarged the penguin pattern, the 150% setting on the photocopier. Some of these patterns are ridiculously small. Perhaps the instructions even say to enlarge, if only I could read Japanese I could tell you. As long as you don't enlarge it by a huge amount, then the change in seam allowance will be minimal. The penguins I made (at 150%) turned out to be about 5.5 inches tall, I think that's plenty small and cute enough.
2. This isn't specific to Japanese softie making, but it seemed relevant here. I make all my patterns on a lightweight interfacing that has a 1-inch grid printed on it. I get it at my local JoAnn's by the yard, it's called Tru-Grid Graph Material. I either trace from the original or enlarged pattern, or freehand if I'm making something up. I just use a ballpoint pen to write on the interfacing. When I'm done cutting all the pieces out, I save them in labeled ziploc bags in case I want to make it again. Wow, this makes me sound organized, doesn't it? Ha! Here's the part where I'm anal: I even trace store-bought patterns, because if I'm making one of the smaller sizes in a multi-size pattern, I just can't handle cutting off the larger sizes, in case I might want to make whatever it is in a larger size later.
3. I used new fabric from the local quilt store, chosen in part for density of weave. In general, the seam allowances are small and some seams can get really stressed. If the fabric weave density is too small (too much space between the fibers), they won't be strong enough to hold the stitching and the seams may pop. On my stretch doggie attempts (here and here) I had several popped seams that I then had to go back and reinforce by hand--and let me tell you that this is hard. You have to either re-sew all around the pop to increase the local seam allowance, or do some fancy stitching to rebuild the shredded fabric. And then it may pop again anyway. Much much much better to avoid this if at all possible. Alison had this problem too, and solved it very creatively by sewing on little fabric bandaids.
4. I sewed one prototype so I could see where the "issues" were. Of course then I needed to remember what the issues were. One I remembered: follow the instructions and don't sew up the back of the head first otherwise there is no way on this earth that you are going to get the body sewn to the head with your sewing machine. I remembered so well because I had to undo the stitching along the back of the head, that helps me remember. One thing that I didn't remember was "attach feet before sewing on the butt". One of the six production-line penguins had to have grafted-on feet (see image above, they're supposed to be sewn into the seam).
5. Backtack, backtack, backtack. At the beginning of stitching, at the end of stitching, when you turn a corner, if the moon is full. Because the seam allowances are so tiny, if you don't secure the beginning and ends of your stitching, they may work their way free once you've stuffed it (or before). Then you'd need to hand-repair (see #3).
6. I triple-stitched critical seams--stitch once, stitch again close to but outside the first stitching, then zigzag.
7. I used a smaller stitch length, "2" on my machine.
8. I tried alternate methods. The penguin feet (and beak) are felt, and there was no way I was going to be able to turn those feet inside out after stitching them. So I just stitched, trimmed, stuffed, and used them as is. I even tried dropping my stitch dogs and free-handing it (getting a little quilting practice in). This change made it easier to cut the pieces out of felt, as I only had to cut out the vague outline of a foot, not the specific waving outline, because I was just going to trim outside my stitching line (wherever that happened to end up) anyway.