Be Brave and do what makes you curious in life, is something I'm always telling people I meet in my life as a dog rescue person.
Do your homework.
When starting to volunteering, start from the bottom in the organisation. Clean the rooms/cages and be around the dogs. You learn so much by observing them.
This is a skill you can do anywhere in life. Observe people. Learn to read their signals and gestures.
If you met a scared dog (scared dogs and humans are what challenges me the most) be calm. He/She is like an angry survivor trying to sniff out where your weakness are. Same goes actually with humans. They feel they need to 'explode' and get more power, your energy.
Find out what makes them scared, you will find their weakness(es).
Even if you start to feel scared/uncomfortable yourself, pretend to be Brave and your brain will believe it. When your brain believes it, everyone else will feel it. You are acting Brave.
Learn to observe (not to judge) and put your energies into Brave mode, and the scared dog will follow you, and believe that you are a Brave Savior.