Literary conventions are the definable features which dictate a text as being part of a particular genre.
Therefore, the literary conventions depicted in Beowulf are ones which support the naming of the text as a heroic epic poem.
A heroic epic poem needs to be broken down so as to examine each part of the descriptive title so as to fully understand why it fits into the genre which it does.
The "heroic" aspect of Beowulf adheres to the Anglo-Saxon characteristics which detail the adventures of a man deemed superior in the Anglo-Saxon culture as deemed important by the culture. Anglo-Saxons raised up men who were warriors, leaders, polished speakers, and fought epic battles (battles fought against a foe who is equal or greater than the protagonist).
An "epic" is a long narrative, derived from oral traditions, which told of the legendary deeds of either heroes or legendary figures of the culture.
Therefore, a heroic epic tells the legendary deeds of a hero, not a legendary figure.
Outside of this, the poetic devices used in the poem, which are characteristic of the genre are the use of alliteration and the kenning.Alliteration is the repetition of a consonant sound within a line of poetry. A kenning is a metaphorical phrase, or grouping of two words (typically hyphenated), which is used to elevate the language and provide for a more imagery ridden phrasing. An example of a kenning is battle-boast which means promise.