Before declining a request, understand what is needed and when. Sometimes a complete report is being requested when a short summary would solve the problem. Ask about the outcome and deadline before committing. This helps you distinguish a request you genuinely cannot take on from one you could deliver with a smaller scope.
Make the tradeoff visible: “I can prepare the client summary by Friday, but I would need to move the research review to Monday. Which should take priority?” If you do not control those priorities, bring the decision to the person who does. Avoid quietly accepting both commitments and hoping the conflict disappears.
Offer an alternative only when you can actually follow through. That might be a later date, a smaller deliverable, or an introduction to someone who has agreed to help. You do not need to invent a solution to justify every no. For recurring requests, establish clearer boundaries around your work instead of renegotiating the same limit each week.
Keep the response short enough that the decision remains clear. Acknowledge why the request matters, state the constraint, and name the next choice. If you tend to over-explain, try the 10-minute rehearsal routine and remove explanations that repeat a point you have already made.