How to Prepare Photos for Posting?

How do you prepare photos for posting?  I have tried to do it using Photoshop Elements 9, both by re-sizing the number of pixels and by coarsening the jpg compression  and the results of both have been unsatisfactory.
Looking at bird photos in this forum, I have been impressed by the detail retained with relatively low pixel numbers and file sizes.  For example, photos posted by Kenn Threed are typically 1200X960 or 1280x960 pixels with file sizes of 200-300 kb and the detail is amazing.
When I reduce the pixel count of my photos to values like this, there is a huge loss of detail even when the jpg compression is fine.   If I leave the pixel count high and coarsen the jpg compression to get file sizes around 600 kb, I can see the jpg blocks of pixels.  What am I doing wrong?
Thanks,

Stephen