1. Headings Make sure they are BIG enough to read. Make sure the color is not too light or matching the back color.
2. Fonts Just because you think it looks cool doesnt mean everyone else does. Makesurethereisenoughspacebetweenwordssonoonehastroublereadingit. Cursive writing is not always professional, its more annoying to read in Powerpoint.
3. Make sure your photos dont take up too much space and go together.
4. Animations Dont over bare your reader with moving objects. Dont make things disappear. Make sure they have time to read the slide before the words go crazy.
5. Transitions If you must make them faster and not drawn out. Not always to people find them cool.
6. Transitions with sound. If it doesnt have to do with the Powerpoint why use it? Try not to make it really annoying.