IWTL how to make my jokes more obvious

I’d love some help with learning how to execute my jokes better so that people actually realize I’m joking. For example, I recently painted my first-ever painting, and as a joke, I asked my girlfriend’s parents if they’d be interested in buying it. My girlfriend later told me it came across as serious, like I was genuinely trying to sell it to them.

I want to avoid situations like this and make my humor feel more lighthearted and clear.