I've always used these prefixes in the following fashion:

Verb:
to un-/dis- (dependent on the verb) [the opposite action of _ ]

Adjective:
dis-ed [the negation of a state of being _ ]
un-ed [the lack of a state of being _ ][is not and never was in a state of being _ ]
-ed [the state of being _ ]

For example let's use "organize"

Verb:
to dis-organize [the opposite action of organizing]

Adjective:
dis-organiz-ed [the negation of a state of being organized]
un-organiz-ed [the lack of a state of being organized][is not and never was in a state of being organized]
organiz-ed [the state of being organized]

Of course as in any language there are exceptions to this rule as well as words that don't fall into every category where we would use a different word instead: for example "dress" and "robe"

Verb:
to un-dress [the opposite action of getting dressed]
to dis-robe [the opposite action of getting dressed]

Adjective:
dis-rob-ed [the negation of a state of being dressed]
un-dress-ed [the lack of a state of being dressed][is not and never was in a state of being dressed]
dress-ed [the state of being dressed]