Having worked for about six years in US Foreign Policy and teaching it for about two years, my response would be, first you must define what "works" means. How are you defining success - either for the beneficiaries of the humanitarian assistance, the loan, the projects to improve economic livelihoods, democracy, etc. or for the US government and what the agenda was through the policy in the first place. It is important to note that every action by the US Government is highly calculated and there is always an agenda behinds what happens or what doesn't happen.
The Bay of Pigs and the war on Iraq were clearly failures.
The other thing to note is that US Foreign Policy changes with each administration, so defining what "works" depends again on the agenda of the new president. Is the improved outcome for the overseas audience or improved perception of the US or is the outcome self-interested for the US?
For me, what works in foreign policy is empowering local populations to create sustainable solutions for improving the quality of life in their countries. When there is too much determined by the US, it is purely neo-colonial and patriarchy at its worst. The newest trends in foreign affairs is trying to at least in appearance empower locals.