The best way to collect textual evidence (quotes, techniques) is to analyse the text yourself.
However, here is a very small list of examples.
Equality/Inequality/Racism
Symbolism/Imagery - Iago's description of Othello as an 'old black ram' and ‘the Moor are now making the beast with two backs’.
Brabantio’s description of Othello: ‘O thou foul thief'
Appearance v Reality
Dramatic irony in the play: Iago’s soliloquys - the audience sees Iago’s honest side while the characters see his deceptive side (even though Iago is referred to as ‘honest’ by the other characters).
In a soliloquy, he states ‘I hate the Moor’ but he appears to be friendly towards Othello.
‘Honest Iago’ is a recurring motif?
Othello perceives Desdemona as being deceitful yet in reality, she is innocent - ’Fetch me the handkerchief. My mind misgives’ (alliteration of 'my mind misgives').
There's a contrast between the two - Iago is seen as honest, yet he is actually lying. Desdemona is seen as unfaithful, yet she is actually faithful.
Othello's Jealousy and Desdemona's Fidelity
- Jealousy is the protagonist's fatal flaw
- Metaphor of the 'green eyed monster'
- Desdemona and ‘The Willow Song'
In the second verse:
‘Let nobody blame him; his scorn I approve’ emphasises her loyalty to Othello, despite his remarks and actions (instigated by his jealousy).
‘I call’d my love false love; but what said he then?/ If I court moe women, you’ll couch with moe men’ - a comparison between the persona and their lover and Desdemona herself and Othello.