Are you sewing it by hand? Because if you are- kudos to you.
You could watch some tutorials on Youtube on random plushies to learn some tips and tricks for shaping and stuffing.
If you're stitching by hand use a blanket stitch (you can youtube if you don't know what that is cuz idk how to explain it)
Stuff the limbs and other external features (e.g. its snoot or tail) individually and when it's time to stuff the body try to ball up a really big amount of stuffing and stuff the torso in one go. This helps prevent the lumpy appearance.
I'd also suggest coming up with a symmetrical design so that when it comes time to sew the 2nd half you've already had practice with the first.
Additionally, if you create it in two halves you can sew them together sagittally and pop the spikey back ridge between the two halves (inside out when you're sewing it together), which will make them seamless.
Then leave the stomach unstitched to reverse it the right way out, stuff it, then fold the raw edges in and blanket stitch it shut.
ONE LAST TIP- make a little paper heart (or clay, or whatever you have available) and pop it in before stitching it up. So you can give your new lil dragon a heart :3