Get to know the Endocrine attendings at your new program. Endocrine is a small world...they all know each other. Case reports and poster presentations are helpful, but send to Endocrine Society, ADA, ATA, or AACE instead of ACP or SGIM.
Become involved in the regional chapter for AACE...easy enough to find that info on the AACE website (look for the Chapters tab and it will show you the regional/state chapters- some are more active than others). If you are in the New England area, there is a New England Thyroid Club as well. Again, Endo is a small world and they all know each other..
Go to the National meetings (presenting a poster is a good way to get the time off and even have your program pay for the trip)...for most meetings it is free for med students and residents to register. The ATA has a workshop for fellows/residents/medical students that is a day before the national meeting and continues through the meeting that includes accommodations and meals...you get to meet a lot of people at these meetings (particularly ATA, its a small group).
If there is endocrine related research (or you can find someone to mentor you), you should try to start early since it can take time to get enough work done to actually publish, but there may be some shorter term projects (or review articles) that you could be a part of that could get you a publication by 3rd year.
Is the university that your program is affiliated with a place with an Endocrinology fellowship? can you do an elective with them? Do this at the end of intern or beginning of your 2nd year...you need to have some knowledge behind you to impress them so wouldn't suggest you do this as a fresh intern.
not sure what 3 half day clinics will accomplish, but when i was a 3rd year, we had to do an additional 1/2 clinic that could be a subspecialty clinic, so that can be nice since it will be in your subject of interest.
Endocrine is particularly friendly to FMGs so you shouldn't have an issue with matching, but it will be important to apply broadly and in large numbers so you can get a good number of interviews to rank (but ROL of 5-7 should give you a good shot). If you are an US -IMG, it can be harder, but still no real fear of not matching if you are realistic.