A study conducted in 1965 identified that argument mapping leads to clearer writing.
Some reporting verbs require a ‘that’ clause, others do not:
Reporting verbs not followed by that are usually followed by a noun phrase. Unfortunately there is no strategy to determine which verbs require that and which do not. You just have to memorise them. The best way to acquire useful reporting verbs is by reading journal articles and academic text books. To get you started, here is a list of common reporting verbs followed by that: