Don't cram too much information, either in each slide, or in the whole talk. Organization - Have a very clear introduction, to motivate what you do and to present the problem you want to solve. Don't put the details in the talk. If you need it to remember, re-state the information a second time.
Good looks are important.
The more you rehearse the talk, the better it will be. A rehearsal is most useful when carried out loud. Text - Slides should have short titles. A long title shows something is wrong. If you have lots of text, people will read it faster than you present, and will not pay attention to what you say.