What have I done in the second slide?
I've used contrast. First, on the background by making it black to make the chart more dominant. Second, I've made the bar showing Obama's Twitter followers red to emphasize the point of the slide. Finally, I've removed superfluous items like grids and the frame around the graph so it doesn't distract the audience from the point.
Next time you watch a presentation (yours or someone else's) try to think about how contrast is being used or not being used... and learn from it!
But I must admit, that even though you know what looks good, it can still be very time consuming to create well-designed slides (even for us). And that's exactly the pain we are trying to help you with.
So, if you don't want to spend time making a bar chart yourself, we have one you can download for just 19 USD - it includes 10 editable bar charts in 3D and 2D. Make sure to watch the video tutorial when you go to the site.