I use bold here to distinct what I am saying from just normal speech. Wasn't really my first choice, I usually go for colors, but I didn't know if we were supposed to use colors so I used bold instead.
Italics is for when I want to make something more distinct. As in, I put weight on a specific word. Like, he just had to kill her, and he just had to kill her with a [i]rollerblade[/i]. For instance.
Shouting is done with capital letters. I AM SCREAMING THIS. For instance.

That's how I do it.