You might have a killer idea, or a punchline, or even a killer facial expression that the greek god of inspiration (whoever he/she is) shot down to you in a lightening bolt right before your scene. You may be so witty and awesome that you know what you're about to do or say will cause 10 people to have heart attacks due to its raw comedic power.
Good for you.
Wait for the right time. And please, don't force it.
I have a strange philosophy that in improv it's better to stand there and do nothing than force an idea down fellow scene-builders' throats. (Obviously it's better still to contribute to the scene). Forcing your ideas in a scene is the equivalent of shooting every time you have the ball in basketball. Although this is great if you're Michael Jordan (and some people believe they are), even Michael Jordan realized he had to pass the ball more often if he wanted to win a championship (or 6).
Same applies to improv. Understanding timing is largely intuitive, but there are some important things to consider. Here's some basics:
- The best jokes have a proper set-up. The best moments in a scene work the same way. The entire scene can't be funny punchlines, goofy movements--that's more akin to clowning than improv. Large percentages will be setting the scene up for awkward or interesting moments.
- Pause before big moments. Nothing ruins a good tension like running right into its resolution. Great orators made decent sized pauses before and after big moments. They were essentially setting up one-man dramas.
- Don't make every reaction instantly verbal. This helps slow things down, which allows the audience and your teammates time to process. Most often they're physical first, then verbal. This will help with good timing.
- Vary the timing in your speech. Say some words slow, other words fast (as it applies to the scene). I knew a girl in high school who spoke as fast as the micromachines guy (see video below). Although I was continually impressed with how fast her mind worked, to keep up with her mouth, there was no drama to her speech--no ups and downs, it was all just really fast.
- Beware of talking too much or too little. Of course, you're going to play some characters that are virtually silent, or motor-mouths. But, by and large it's a good starting rule to think about saying one to two sentences, and then allowing other scene partners to add something.