I started using a thumb pick about 5 years ago after being basically a 100% flatpicker for 15 years. What a weird feeling! I have to say it took probably close to one year before I felt anywhere near comfortable using a thumb pick to play in front of anyone, but now after 5 years I am so glad that I finally taught myself how to use one!
For help on choosing a pick check out these articles: Guitar Thumb Picks Review and More On Guitar Thumb Picks.
One of the main reasons that it took me close to a year to feel comfortable with my thumb pick is because I didn't take the time to slowly build up a good technique and spent too much time working on tunes that were too hard for me to play at the time. One of the most important things you can do when learning to use a thumb pick is to go very slowly, concentrating completely on making a small motion and just working on one or two strings at a time, developing a good attack with a clear tone.
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