The surest way to learn that flat felled seams start with the allowance to the outside, face side, of the garment, is to sew a seam and see that you've got it backwards. After carefully picking out tiny stitches from silk brocade I started again.
So, I laid the pieces together, face sides out, sewed a seam with a 1/2 inch allowance, and trimmed one side of the allowance to just under 1/4 inch.
Then I folded the larger allowance over the trimmed side and pressed. I did this before pressing the seam open because I figured it would be less fiddly.
After pressing the pieces open I stitched 1/16 from the edge of the fold.
Here's the seam from the back.
And from the front.
A very pretty seam!