My advice is set a price that you are comfortable with on the airline price that you want and when you see a price that falls into that comfort zone, BOOK IT. The trick is to keep checking different sources and check them often. They change often, sometimes within minutes. You may well see it for less at some time in the future but if it did fall into that price zone you felt comfortable with, then what the heck.
It is the old adage. "No matter what you will usually find it for less later but many times you don't."
If you are using Priceline for your hotel then you can't cancel but I have yet to regret using Priceline for a hotel booking. Except for the first time I used it and the I had no idea what I was doing.