Y is for Yes
If you desire to improve your speaking skills, and I assume you do if you have made it this far in The ABC's of Speaking, then you must speak. Say "YES" to every opportunity you can find to address an audience. The more often you speak, the more comfortable you will become and your experiences will help you fine tune your oratory skills.
Let people know that you are available to talk to their company, association, conference, club, or other group. Be clear about your range of topics and be excited to be asked to speak to crowds of all sizes.
The skills it takes to be on the big stage speaking to thousands of people are both the same and different from those needed to speak to half a dozen. The only way you will know how to react to different audiences is to have hundreds of presentations under your belt.
Do not over think the opportunity or pre-judge the group. Your goal is to get the stage time (See "S is for Stage Time"), and thus you should be excited about every chance you are given to speak.
Making yourself available and agreeable to speak will be part of a continuous cycle. The more you speak, the better you will get at speaking. The more you say "yes" to speaking, the more organizations will pop up with invitations for you to speak. Do not rationalize that you might become "over-exposed" in your city if you speak too often. If you are good, and have a powerful message that is important to people, smart groups will invite you to speak.
Have A Great Day.