Hey there girls :) Yes, you do need to be warm to do stretching...muscles, as Veena said, are like cheese: they crumble easily when they're cold, and they stretch when they're warm! It's far easier to injure yourself from stretching when you are cold.
You could take a nice hot shower, or whatever you like, as long as you feel nice and warm when you're stretching!
As for things to do...while I love Yoga, and the idea of it, I don't really feel that I have the time. Perhaps one day I will work on it when I have a little better of an understanding about my time, but for now...I'm just plain old stretching when I work out!
The most improvement I've seen is in my hamstrings, which I've been stretching almost every day, IN the shower. Put my leg up on the back part of the bathtub, and just lean over it, slowly. I'm warm from the shower, the tub wall is a good height for me, and...well, it just worked!
Otherwise, you can look up all kinds of stretches online, and just work them into your normal routine. It doesn't have to be anything fancy...just something to get the job done, if that's what you want!
Also, Veena has some stretches on here, and they seem good. :)