Rabbi Eli Melech’s Tzetel Katan recommends that someone who is shy practice praying in a loud voice for 40 days. He says that you should say the blessing over the Torah in a loud voice as well. I have made this a practice, and noted some benefits:
1) By saying Boruch Hu U’Voruch Sh’mou and Amen more forcefully after the chazzan rather than just mumbling it, I get more people at the minyan to say Amen.
2) By projecting more confidence, I seem to be getting more aliyot.
3) Outside the minyan, I find myself speaking up more.