Okay, so I totally caved and decided to try my hand a little more at this, in case anyone wonders how I do what I do. Especially since a lot of you are using or have used banners and icons I've created 
We start with an icon of Miracle Laurie (Dollhouse) that I found through Google Images:
So the first thing we do (after opening Gimp, of course) is choosing our size. I tend to always go for 200x200, even though they are technically 100x100 on this site, because it gives a much better quality in the end.
I then pick the photo up from my desktop and drag it into Gimp, where it starts off very large
The first thing I do (if the image name off to the side is bold) is right-click the square and choose 'Add Alpha Channel'.
Now, I re-size. Again, I right-click the small square at the left side of the screen and pick 'Scale Layer'. By now, I can usually do it on the first try, but you can play around with the size as you'd like it. Just remember, don't re-size and already re-sized photo; instead, go Ctrl-Z (or Undo) to get it back to normal and then try again. Otherwise, you'll ruin the pixelation of the original photo.
Now, I don't usually zoom in for an icon (unless I'm erasing part of the picture) but I did it now so you can better see what's happening. I've re-sized it as I want it and am ready to continue.
Thanks to this site changing to round icons, my next step is to grab the Ellipse Select Tool and frame the photo with it, so I can tell what it will look like when used on the Boards.
I move the photo around until I find exactly the right spot that gives me what I want (I'm a fan of half-a-face icons, lol).
And then you right-click the image once more and pick Layer to Image Size.
Now, if the image you have is just a little too dark, here's what you can do; again, right-click the small image and pick Duplicate Layer. While on that layer, you pick Mode (just a few inches above the small images) and choose Screen. This will lighten it up. If it's too light, you can adjust the setting at the Opacity option, right between the images and Mode. You can also duplicate and screen it more than once after you've merged the 2 layers. I only did it once and at a 50% opacity. I also followed it up by merging everything together into just one image.
This next part is something I do to everything I make, including banners. No matter the quality of the photo (though occasionally I've found it unnecessary, rare as it is) I go to Filters and under Enhance I choose Unsharp Mask at the very bottom.
When I get to Unsharp Mask, I do not alter any of the settings; I just press OK. Feel free to play around with it yourself, I just prefer the main setting myself.
Now, because the pictures I use are rarely HD quality, I return to Filters->Enhance and this time pick Sharpen.
Sharpen starts off at 10 and, again, you can play around with it. I usually pick 40, though.
I like to add bright bangs of color to my images, so the next step is to go into Color and pick the first one, Color Balance.
Again, you can play around with it. It usually takes me at least a few tries to find the one I'm happy with. You can reset at any time.
After playing around, I've found my happy finality
Almost to the finish line, I head back into Filters, go into Blur and pick Selective Gaussian Blur.
This step will start at 5 on both counters. I use 5 when I really want something blurred out, but if I just want to blur out some pixelation from my editing, I'll press down twice on both picks, so it looks like this.
And this is what it looks like!
Then I just export the image to png (or jpg, if you prefer) and you've got yourself an icon!
Here's the before and after, side-by-side:
------->>>
Hope you can use this
We start with an icon of Miracle Laurie (Dollhouse) that I found through Google Images:

So the first thing we do (after opening Gimp, of course) is choosing our size. I tend to always go for 200x200, even though they are technically 100x100 on this site, because it gives a much better quality in the end.

I then pick the photo up from my desktop and drag it into Gimp, where it starts off very large

The first thing I do (if the image name off to the side is bold) is right-click the square and choose 'Add Alpha Channel'.

Now, I re-size. Again, I right-click the small square at the left side of the screen and pick 'Scale Layer'. By now, I can usually do it on the first try, but you can play around with the size as you'd like it. Just remember, don't re-size and already re-sized photo; instead, go Ctrl-Z (or Undo) to get it back to normal and then try again. Otherwise, you'll ruin the pixelation of the original photo.

Now, I don't usually zoom in for an icon (unless I'm erasing part of the picture) but I did it now so you can better see what's happening. I've re-sized it as I want it and am ready to continue.

Thanks to this site changing to round icons, my next step is to grab the Ellipse Select Tool and frame the photo with it, so I can tell what it will look like when used on the Boards.

I move the photo around until I find exactly the right spot that gives me what I want (I'm a fan of half-a-face icons, lol).

And then you right-click the image once more and pick Layer to Image Size.

Now, if the image you have is just a little too dark, here's what you can do; again, right-click the small image and pick Duplicate Layer. While on that layer, you pick Mode (just a few inches above the small images) and choose Screen. This will lighten it up. If it's too light, you can adjust the setting at the Opacity option, right between the images and Mode. You can also duplicate and screen it more than once after you've merged the 2 layers. I only did it once and at a 50% opacity. I also followed it up by merging everything together into just one image.

This next part is something I do to everything I make, including banners. No matter the quality of the photo (though occasionally I've found it unnecessary, rare as it is) I go to Filters and under Enhance I choose Unsharp Mask at the very bottom.

When I get to Unsharp Mask, I do not alter any of the settings; I just press OK. Feel free to play around with it yourself, I just prefer the main setting myself.

Now, because the pictures I use are rarely HD quality, I return to Filters->Enhance and this time pick Sharpen.

Sharpen starts off at 10 and, again, you can play around with it. I usually pick 40, though.

I like to add bright bangs of color to my images, so the next step is to go into Color and pick the first one, Color Balance.

Again, you can play around with it. It usually takes me at least a few tries to find the one I'm happy with. You can reset at any time.

After playing around, I've found my happy finality

Almost to the finish line, I head back into Filters, go into Blur and pick Selective Gaussian Blur.

This step will start at 5 on both counters. I use 5 when I really want something blurred out, but if I just want to blur out some pixelation from my editing, I'll press down twice on both picks, so it looks like this.

And this is what it looks like!

Then I just export the image to png (or jpg, if you prefer) and you've got yourself an icon!
Here's the before and after, side-by-side:


Hope you can use this

Willow Tara
Thanks so much for this!!!! Now I need banner stuff! Mainly how to get more than one pic merged into... Well one pic as a banner...