I have an older tutorial here on cutouts: https://oh-crime.dreamwidth.org/32608.html

textures help, and a line around the subject and then blurred is also good, i think the ones you've given aren't so bad (we are our own worst critics) and have great colouring!

the other thing i do is to cut it out at size, or 200x200px before resizing it down - it makes it better in general