To decide on a topic:
Choose a topic that interests YOU.
The best way to get this right is to really use your own imagination to see what you respond to. Your first tries are important. You can narrow them down later.
Once you start to narrow your topic, finding the right keywords is important. Don't be afraid to let your topic change as you do more research. Note: when the narrator says "one search" what she really means is "Article Quick Search"
If you cannot access the above video, you can watch it here