Communication is key when making use of Thresh's lantern. Let your teammates know how you like to use it.
Death Sentence and Flay can be combined in either cast order for powerful combinations.
Thresh can collect souls without needing to kill units himself. Planning your map position to be near the most deaths will help to maximize soul collection.
Thresh's Death Sentence has a long cast time. Watch for the cast to begin to take evasive actions.
Intentionally breaking a wall of The Box can allow a vulnerable ally to escape unscathed.
Thresh relies on collecting souls for a portion of his defense and damage. Try punishing him when he moves to collect them.