Once you've assembled a pattern, you need to refine the pattern so that it is a precise fit to your body shape. If your character has padding, you need to create that and then tailor the pattern so that it matches the modified body shape.

The best way that I've found to tailor a pattern is to put it on inside-out. Wear the costume with the seams on the outside, where you can reach them. This gives you (or, better yet, someone assisting you) the chance to pinch and adjust the seams to improve the fit. As you tighten seams, pin them with safety pins (or straight pins if you're more daring).

Once you've adjusted a couple seams (don't do too much in one fitting), take off the costume and sew these modifications. Sew the seams along the pinned line with a single straight stitch. Refit the fursuit to check that the modifications are correct and an improvement; then you can go back and sew the seams again, using a heavier zig-zag stitch with some backstitchig for security.

After a bit of work, the costume pattern should be properly tailored! If you've been working with a test version sewn in cloth, you now need to transfer the changes back to the pattern pieces so you can cut the fur.

If you are tailoring a fur version (an option which is a good time-saver if you don't plan on reusing the pattern in future costumes), you will need to cut the extra fur after sewing over the seams. Once the inside excess fur is removed, the seam should press rather flat. Be careful if you don't sew practice patterns before using fur; a mis-measured or misjudged pattern can be an expensive mistake.

Once all the seams are sewn in the fur, go back over them with a pin to "pick" the seam. Use the pin to slide in under the fur fibers sewn down into the seam and then pull upwards to loosen the fibers. This will help the seams blend away into the fur; if done carefully, this can make seams in a moderate or long shag fur almost undetectable.