Better is not an instruction
'Better' means nothing to a model, so it defaults to longer and more florid, which is worse. A resume bullet has a known good shape: action verb, technology, measurable result. Describe that shape and you have replaced a preference with a specification.
Show one bullet in the target form
One example does more than three sentences of description. 'Cut checkout latency 40% by migrating the payments service from REST to gRPC' tells the model the verb placement, the level of detail, and where the number goes — all at once. This is the cheapest few-shot you will ever write.
Say how many, and say nothing else
Ask for 'exactly three bullets as a markdown list and nothing else'. Resume prompts attract commentary — the model wants to explain its choices. Closing the output format shuts that down.