When sewing items up, I never use a knot. I always leave a tail length which I over sew into the stitching up of the item as I am sewing it up. I have taken some picture's for an illustrated tutorial.
Beginning with inserting your needle where the sewing up is needed.
I've pulled the needle through and left the tail I will over sew into the sewing up of the item.
Now I will begin to sew up the item.
Here I have done one sewing st, which included going over the tail.
Here I have progressed even more with the sewing up and also sewing over the tail.
I have almost reached the end of my tail, which will be out of site very soon. A tip is to slightly stretch your work through out the sewing up process, so the sewing is not too tight
You can see here where the tail has ended and I am now at the end of my sewing row, but it does not finish here.
To hide and re inforce your sewing ends, we are going back into the sewing we have just completed.
I have gone as far as I feel I need to here.
Now I am going in the reverse direction once again, for more re inforcement.
I am now satisfied with the re inforcement and will just snip off the yarn.
Here it is all finished and no tails or ends to be seen and not a knot was used!
What I have done here is not as neat as it could be, one the colours being different and two taking the picture's whislt working. But I hope you get the gist of it and try it for your self some time. This method can also be used with a small crochet hook, but that's another lesson.