What do you want the report to show?
If for example you want to see a distinct list of all open incidents then you need to exclude the data/fields that are not unique. This will include things like the contacts of the incident and the assigned group etc. as in most cases this will contain more than one value and will therefore appear in the results more than once.
Alternatively you can group by those fields so you can then ignore groups that you are not interested in but this won't 'clean' the results instead it will present them in a managable way.
If you want to have a report that shows a specific set of data then you are probably going to be better off creating your own report but this does rely on you knowing exactly what data you want to see.
If you can be specific then I'm sure someone can help.