For me with signalling the key was totally practice. I had horrible trouble with it at first, but after a few months of cycling every day I found that I was signalling with much less stress. Practicing off-road etc sounds like a good plan, though, to accelerate the process! It's a really good idea to signal if you can, and if you can't then a) you need to be keeping a much closer eye on traffic because they won't know what you're doing, and b) don't take any risks with your turns at all.

There's one turn on my route home from work that I really can't signal on - it's at the bottom of a very steep and narrow hill, and I'm always fully engaged in braking with both hands, but I've never actually had a problem there (so far!).