Why do people really volunteer? A good question, and everybody has their own reasons, but for the most part I've found that most dedicated volunteers do so because they enjoy it. It's very simple it gives them fulfillment, maybe they get some respect and honor too. But it helps a lot if you like it.
As for your approach it's certainly a good start. It's probably a good idea though to volunteer in an an area that you are passionate about - be it literacy, environmental, pro bono legal work, etc. etc.
And as far as doing so for your MBA, there are basically two types of volunteer positions 1. regular volunteer 2. leader of volunteers. If you can, work your way up to number two
(Which will be easier if you choose something you really like)
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