The images below display a mix of hard and soft edges. This exercise will produce a device that helps you decide where you want the specificity that hard edges provide and where you prefer the generality of soft edges. The concept is simple; paint a version of one of the selected images using only soft edges.
When the painting is dry you can look for places where you really want hard edges. Be conservative, choosing the places that you feel most require hard edges. Paint the hard-edged shapes right over the initial soft ones. stop after each hard edge and stand back a little, to get some distance on the big picture. Just because a shape has hard edges in the photo doesn't mean the painting needs them, too.
You may have to wet both sides of your paper to get it to stay wet longer.