Indians usually have the habit of adding the reflexive pronouns 'itself' for emphasis e.g. "I wrote to David yesterday itself" - 'I want this done today itself' etc.

Could some native English speaker guide me as to how to bring about a stress in such statements?
If your native language does not create such stresses through raising the voice, i.e., speaking more loudly on the stressed word, it may be difficult for you to switch to this mode of stress. Nevertheless, it is the most common way to stress an indivual word in English. Raise your voice on the stressed syllable of the word you want to emphasize.

I wrote to David YESterday. I want this done toDAY.

Emphasis through the addition of other words or by changing the word order is sometimes possible.

I wrote to David only yesterday. I wrote to David just yesterday. I JUST wrote to David yesterday. It was only yesterday that I wrote to David. Yesterday was the very day I wrote to David.

I want this done by close of business today. (at the work place).
I want this done before the end of the day.
I want this done this very day. (awkward, unidiomatic, not recommended)

I need this done NOW.
I need this done right now. (American)
I need this done right away. (American)
I need this done as soon as possible.
I need this done at this very moment. (awkward, unidiomatic, not recommended)

I saw it all happen HERE.
I saw it all happen right here.
I saw it all happen in this very place / at exactly this place.

In the case of people, the reflexive is fine.

I spoke to Mr. Sorensen himself. The teacher herself has said so.
Mr. Sorensen was the very person I spoke to.
The teacher is the very person who has said so.
It is that very teacher who has said so.
Students: We have free audio pronunciation exercises.
I am indeed grateful to CalifJim for this excellent and elaborate answer. I am sure many Indians and other non-English speakers will immensely benefit by this. Thanks again.
My pleasure.