A good slideshow isn't just a bunch of slides; it needs to have a definite beginning, middle, and end. In other words, there should be distinct groups of slides focused on specific topics or themes.
Note, many of these tips will also work in Powerpoint, just some of the locations and names may be a bit different.
The light table can be found by using its option under the View menu. Here you can change the order of your slides just by dragging them to a new position. By shift clicking on multiple slides you can then move a whole family, or section of slides to a new location. In Navigator mode you can also create parent and children slides. If you move the thumbnail of one slide to the right, you can then change the order of the slides. It becomes a "child slide" to the slide above it. Child slides can be toggled in and out of view by flipping the small black triangle that appears next to the "parent slide" above it.
One thing you can do is to create a parent slide with a sub-sectional title and then place a number of child slides bearing the actual content for that sub-section underneath it. As an example, you might have an introductory sub-section framing the questions being discussed in the presentation, another containing your data, and then a third summarizing your conclusions.
New slides inherit their position in this hierarchy from the slide immediately above them in the navigator. However, by pulling new slides to the left or right in the navigator, you can change their position, turning a child slide into a parent. You can also move slides from one group to another, or, by Option-dragging, duplicate them.
Another view you can use in Keynote is Outline mode. I don't use this one a lot but it is useful for creating a fast outline of your work. One reason I do not use this mode often is because I don't make slides with a bunch of text or bullets, so for me outline mode is not always effective. But if you plan to make a bullet-point riddled presentation this may be a good option for you. It will allow you to type in and format your text in the outline, then the application will convert it to a slide for you.
These are the main functions of the different views in Keynote. Powerpoint will do most of the same things, Microsoft just calls the views something different.