It is ideal to walk around the event venue before the event starts and write down appropriate ISO, shutter, and aperture settings for each part of the location. This is done so you can adjust your camera quickly by using a “cheat sheet” of sorts. Keep in mind that this "cheat sheet" may also only turn into a temporary reference guide if you are not shooting in controlled environments (outdoor events). Using the paper and pen method usually only works when shooting events that have a slower-paced environment. When shooting more intense events, it is a good idea to memorize exposure settings and learn how to improvise. If you can do it all mentally, it is not only faster but will slowly develop a sense of light over time - which is obviously a great skill for any photographer to obtain.
It may take a little time to mentally adjust but the main thing you'll need to get used to is knowing how to configure calculations in your head at a faster-than-average rate. You'll need to understand how to effectively make up for light loss, or how to effectively cut exposure down with ISO speed, shutter speed, aperture, etc. This may sound difficult at first but after doing it for an hour or two it becomes very easy and should be no problem if you know what you're doing. When shooting events professionally, it is usually (keyword being "usually") not a good idea to set anything on your camera to "auto" unless absolutely necessary. Your client is paying you for your photography skills, this entails not only composition but an understanding of how exposure works. After all, anyone can go around with a camera set to auto and take pictures!