Whatever order or structure you use in your presentation, it's important that you tie the different segments together with segues. (Of course, as with anything, there are exceptions ― you'll look at one in a moment.)
A segue is a word, phrase, or even complete sentence that provides a smooth transition from one segment of your speech to another. (The old Monty Python TV show poked fun at segues by connecting scenes with the pronouncement "And now for something completely different....", which is a segue that is also a kind of anti-segue.) Segues make it easy for your audience to follow you as you move from one thought to another.
A segue can be as simple as a single word. However, (note ― "however" is a segue) one type of segue that is sometimes overused is the connective word (principally 'and' and 'so'). It can be annoying when you hear "I went to the market and I discovered that the soap I wanted was on sale. And even though I didn't need that much soap, I bought two boxes. And then I came home, and who do you think was there?" Similarly, "So he came up to me and asked me my name. So I told him to go away. So next thing I know, he comes up to me again. So I said...." is overkill.
I want to stress that's there nothing wrong with the occasional and appropriate use of 'and' or 'so'. They're effective ways to tie thoughts together and to segue from one sentence to another. But the overuse of these connective words is distracting.
You already use segues in your everyday conversation, such as "the next thing I knew...", "but that was just the start of my problems...", "I should have guessed what would happen next...", or "speaking of coincidences, yesterday I ...." So when you're writing a speech from start to end, you'll probably produce your segues automatically.
But if you're inserting something into your speech, it's easy to insert a thought without thinking about the segue into (or out of) that thought. Just be aware that this might happen, and insert segues as needed.
Segues should be used to help your listeners easily follow you. But there are occasions where you deliberately don't want to use a segue. Doing this provides a break in your narrative and can be a great attention-getting device.
For example, in my TEDx Talk, I was describing a problem that we have in our society ― many adults no longer pursue their dreams. I then paused for several seconds before I continued with "The world recently lost a great man, Muhammad Ali." There was no segue between those two thoughts, which made people wonder (I hoped) what the connection was between the problem and my next statement, and so they listened more closely (I hoped) to what I was saying. (The long pause I had before I started my next thought emphasized the break in what I was saying.)
While it's great to get the audience's attention like that, it's not good to confuse them or leave them hanging. So I promptly continued with "Muhammad Ali was a champion athlete, but he was also a champion dreamer." Now I've tied in Muhammad Ali (a dreamer) with my previous thought (many adults don't dream). My audience didn't know exactly what the connection was going to be, but they suspected there was one. So although I didn't use a segue, there was still a logical transition from one thought to the next.