This post is regarding recommendation letters (LoR) for residency in the USA:
You need at least 4 LoRs.
LoRs from US physicians are of more value than from letters written by docs in Saudi.
The ERAS system allows you to upload the letters yourself or ask the doc to upload it for you to your account directly. The one you upload yourself has a low value. The one the doc uploads can be "waived" or "un-waived". Waived means that you waived your right to see the content of the letter which makes it much stronger. I personally recommend that you waive your letters.
To get a strong letter is obviously only possible by hard work and proving yourself during your rotation.
Let the doctor know that you would like a LoR halfway through your rotation so he's more observant of your performance so he will have something to write for you at the end of your rotation. Try not to mention the LoR at the very beginning of your rotation.
One important tip is that you inform your doc not to mention a special interest in a specific specialty, so you can use the letter for more than one specialty when you apply for residency. For example, you don't want your letter to say " Hani has a very special interest in general surgery" because this way I will only be able to use this letter to apply for surgery and I can't use it for internal medicine. The letter should be more general and talks more about your knowledge and hard work.