[BretWeir]

If these problems are happening in mostly social situations, maybe you've been conversing at a higher level then expected?

I.e., if you're giving a dissertation talk, then complex ideas and intriguing thoughts are par for the course. But if you're chatting up a chick in a bar, then a discussion of string theory/Kant's categorical imperative/whatever deep thought you've been having lately (and many are less profound than these examples) probably won't be fully understood no matter how eloquent you are. It's a matter of calibrating your conversation to the audience. Seriously -- 90% of what we say to other people doesn't really mean anything at all; it's just verbal filler designed to build comfort and rapport. If you're looking to transmit ideas with everything you say, you're setting unrealistic (and unattainable) expectations.

A few ideas that might help things along (most of which have been mentioned by others before):

1. Read and talk -- a lot. When you read, think about how the author uses language to communicate ideas. When you talk, think about *nothing* -- just let it flow. It'll feel strange at first, but the point isn't to sound smart or to communicate ideas; it's to get in the habit of speaking. At some point, it becomes second nature.

2. If you're really having a problem in casual conversation, think of 4 or 5 interesting stories about your life and experiences. If it helps, write them out. You now have a bunch of conversation fillers that you can bust out anytime you hit a conversational lull. You don't need to memorize them word for word -- just the general idea, and fill in the details as you go along.

3. Slow down! Most people I know who have difficulty speaking either feel that their words outrace their ideas, or vice versa. Really, these are two sides of the same problem. If it's the former, then just pause long enough to picture the words in your mind before you say them. If the latter, then try to slow down your thought processes, and communicate just one idea at a time. Often, the conversation will stray, and you won't be able to communicate the whole idea you had in mind. That's fine! Again, outside a professional/academic setting, talking isn't mostly about communicating ideas, it's about creating comfort and rapport. Don't force the issue.

4. If you really want to improve fast, then something like Toastmasters or another "forced speaking" activity is a great bet. Just being forced to stand up in front of an audience and communicate breaks down many of the anxieties that tie peoples' tongues in everday situations.