This is what I do, and I think I get good outcomes.  I am self-taught as well.

I save my original as a .psd file, then I ...

Go to "Save for Web" and select:

Optimize tab

JPEG
Maximum
ICC Profile
Image size tab, adjust size to 200 or 199 on the largest of width or length, with constrained proportions checked
Quality:  Bicubic

(I use "Uncompensated Color" in drop down box when I click little arrow top right side of image window)

Now, check the size of the file.  If it is over 15K, move the quality slider down until you get to 15K or less.
Save as thumb.

I also save my gallery image in the same manner, adjusting it to the Image Size I want and adjusting quality slider if necessary.  I usually don't have to adjust it very much, if at all.

Whether this works for you I can't say.  Sometimes there is a difference in the profiles one sets up, and of course images.  I had trouble with colors and ended up with this configuration.  It solved my problem.  You can take what will help you and forget the rest.

Good Luck!

“Music is harmony, harmony is perfection, perfection is our dream, and our dream is heaven”
Henri Frederic Amiel