How to do a flawless and natural presentation?

A natural presentation comes from practice, and lots of it.

From practice comes confidence. Excellent speakers rarely have more than a few words bullet pointed on their slides. This means that the audience's attention is focused on the speaker. The speaker then tells the audience what the speaker wants them to hear, or directs the audience's attention to an image displayed on the screen.

Aside from not splitting the audience's attention between speaker and loads of text on-screen, having few words on your slides means that you are not tempted yourself to read your presentation to the audience. Such recitation is only suitable if you are analysing the text itself closely.

Further to that last point, having only single or few key words on your slides forces you to know your subject and what to say on each point. You don't have the slides to fall back upon, allowing you to lazily read them to your audience.

Which brings me back to practice. One way of getting familiar with what you want to say on each point is to write down a few detailed notes for yourself. When you practice your talk, you can refer to these detailed notes. Next time through, distil your notes down to only a few key words. Next time through - or when you are confident - your notes should be only the key words on the screen for the audience, and are therefore redundant. No notes, fluent delivery.

Question: What background / foreground things do presenters do that make their presentations flawless and natural?

I don't think I've ever seen a flawless presentation by the way ... much like I've never seen a flawless conversation.

In any case, I think if you do not have a lot of experience, as ff524 says (edit: and Nicholas), practice is important. In particular, if you are going to present at a conference, for example, try present in front of (and get feedback from) your colleagues.

With more experience comes more confidence. With more confidence, presentations become less about "speeches" or memorised text and more about having a conversation with the audience.

At this stage, when you prepare a talk, you can imagine the flow of exposition, how the slides should be ordered, what the audience will understand at that point, what questions they might have and how they could be answered, how to order the points of conversation, how to clarify the "why" before the "how", how to ask the question and engage the audience's curiosity rather than just provide the answer. When you deliver the talk, you have the outline of the conversation you're about to have and you follow through with it, improvising the exact phrasing as feels right.

For me, it often helps to think about the audience as one person that I'm trying to engage with. An audience can be daunting -- a blur of faces -- but if you rather think of trying to engage directly with that guy/gal who came in late and is sitting right at the back of the room ... and make it almost more personal ... I think this is the attitude to have. (This is orthogonal to memorising exact phrasing, which I often find leads to unnatural talks. Having a few nice catchy phrases is nice, but they'll stick in your mind naturally when you prepare the talk.)

There's a lot of great answers here, and most of them say practice. Well, I agree, but I didn't see this particular point in any answer yet, so let me try and explain what usually helps me "keep the flow" and how.

Well, it's all about practice, but:

• when I write the slides, I always have a rough idea of what I would like to say and try out a few (different) phrasings in my head (only the key points / words end up on the slides)
• (ideally), I do multiple rehearsals, improvisation-upon-improvisation. At this point, it is not uncommon for the first rehearsal to last 4 or 5 times as much as the allotted time.
• at early-stage rehearsals, I will try multiple phrasings for the same slide. If I start saying "Um...", my sentences get lost in the middle or something similar, I will just calmly stop at this point and try a new approach to what I want to say.
• I tend to do around 2 more rehearsals after I get the presentation down to the allotted time (for me, personally, going on much longer I might unintentionally shorten the presentation too much)

• now, what, concretely, I get from all these rehearsals is multiple, different ways to handle every slide.

  The reason presentations sound flawless is because not just every sentence by itself is good, but the transitions between sentences, slides and sections are well done.

  And, after doing 4-5-6 rehearsals for the presentation, you know multiple ways to say each thought, and then multiple ways to transition to the next thought, and even if you "slip" and say something other than the "perfect, planned version", you still have a rehearsed back-up strategy.

• as for writing down the notes, I usually sit down after a rehearsal number 2 or 3, and focus only on difficult transitions.

  If, in those few first rehearsals, I sill didn't find a fluent way to say something, or if I did but I stumbled around it, I will try and write down verbatim what I want to say, sometimes even multiple versions.

  Just writing it down usually helps, but if I'm going to go over any notes minutes before presenting, these are going to be it.

• finally, making a rehearsal if front of a test-audience helps. I dread anybody hearing me on the rehearsal number one or two, but I like for somebody to listen on around the pre-last rehearsal.

  By this time, I usually "know" my presentation well enough so I can easily integrate suggestions in, but I still have a go to test if the suggestions fit fluently.

• this all helps the presentation sound more natural. Since you can handle multiple "lingual" situations, you do not sound like you're reciting by heart. On the other hand, you're sure that you have multiple "fallback" options which allow you flexibility and that all of them will deliver the same idea.