Using GIMP to Mask with Soft Edges

[WeegieMovies]

Hi all,
Looking for a bit of basic GIMP advice (yeah I know I should be using photoshop by now, but whatever).
In my thumbnails, I like to cut out an image or two, usually of myself, to stand out against a simple colour gradiant. See my image included as an example.
However, to me the free - selected edges look a little too rough, like it is a paper cutting made with scissors or something. Does anyone know a way to soften the edges when masking an image? I think it would look a lot nicer.

Thanks!

Lee

Example thumbnail;

 

[WeegieMovies]

Anyone got a suggestion for this? It'd be really appreciated! Thanks

 

[Crown]

I've moved your thread to the channel design forum.

 

[QuickTutorial - OS]

If you use the Fuzzy Select Tool, you can set a radius with the Feather Edges option.