Most if not all the stuff I do with gimp is hit or miss. I'm often flying by the seat of my pants and doing this and trying that, to make things look the way I want them to.
The pills were made very simply by first drawing the basic shape with the

and using some

and adding some noise filtering, with lots of

and

here and there. Duplicating some layers and trying out different layer-modes to see what works best.
The glass of water was made in the same basic way as the pills, but I used a blur and some bump mapping, then using curves to give the glass it's look. I had to erase most of the effect created by the curve to get it to look more like a glass. Then it was a matter of just overlaying a gradient or two and trying out some different layer-modes.
The thing with me is that I sometimes can't reproduce the same exact thing twice. Maybe if I wrote down what I was doing or have done, them maybe I could do it again.
Another thing I do is when something is finished, I save it as a png most often. I don't save a lot of xcf files, unless I need to go back to an unfinished image that needs more work.