Anything listed under a Hit: section occurs on a successful attack.
Anything listed under a Miss: section occurs on a failed attack.
Anything listed under an Effect: section occurs. Period.
Some of the original powers had effects that were only on a hit. Those are easy to pick out because they are indented under the hit line. For example:
HIT: blah blah blah
EFFECT: blah blah blah
That type of effect happens only on a hit.
The most thourough example I can think of is:
HIT: This happens on a hit.
. EFFECT 1: This is an effect that happens only on a hit.
MISS: This happens on a miss.
. EFFECT 2: This is an effect that happens only on a miss.
EFFECT 3: This is an effect that happens regardless of a hit or miss.