A lovely piece of advice I came across from Larry King in his book How to Talk to Anyone, Anytime, Anywhere:
If you're about to give a public speech and you don't have much experience (and are thus anxious), come out and state as the first thing (something like) "Hey, I don't talk publicly and this is scary, but I'll try my best".
This immediately can make you less anxious as any mistakes you make can be understood (rather than criticized) by the audience.
When commenting outside my area of expertise I often mention my lack of qualifications so as to invite gentle corrections to my mistakes (and to make others not assume I speak from great knowledge).
If you're about to give a public speech and you don't have much experience (and are thus anxious), come out and state as the first thing (something like) "Hey, I don't talk publicly and this is scary, but I'll try my best".
This immediately can make you less anxious as any mistakes you make can be understood (rather than criticized) by the audience.
When commenting outside my area of expertise I often mention my lack of qualifications so as to invite gentle corrections to my mistakes (and to make others not assume I speak from great knowledge).