A story from when DH was still Fiancee. He'd ask me something like 'hey, do you want some chocolate?' well, yes, I wanted some chocolate. His response 'can you also buy some licorice for me while you're buying chocolate?'
It was a sort of joke, but also sorta serious, because he really wanted some licorice. The first time I bought chocolate and 'forgot' the licorice. He looked sad and I shrugged. 'well, when you'll pick up the licorice I forgot, can you also buy the marshmellows that I feel peckish for now?'
The second time he tried this, I told him that I'd only do him favors like that if he asked for them directly. Worked like a charm.