1. I'm [so] cold. - Get a jacket or sweater on, you stup! If it's Winter, it's going to be cold. If it's Fall, it's going to be cold. If it's Spring, it's still going to be cold! It's not that hard to dress to the seasons!
2. I'm [so] tired. - Go to bed earlier, smarty pants. Nobody cares, especially when you're 'so tired' every day.
3. I went to bed so late last night. - You're a teenager, everybody goes to bed at midnight. If it affects you so much, go to bed earlier. If you want to make a bigger impression, go to bed at three in the morning and brag about that the next day. If you need more sleep, get it. If you need to brag, pick a better topic. End of story.
4. Watsup. - Not much, you? Same. Cool. Mmk, 'nuff said.Let's move on, shall we?
5. How are you? - How is someone supposed to answer that? If you say 'good' it sounds like you don't care and the conversation pretty much ends, even if you do feel 'good'. And someone who's really feeling like crap likely wouldn't admit to it unless they're really bold and need to vent.
An boring but easy way to start a conversation: ask them what they did last night and get details. Listen, ask, listen, ask, listen, ask. It can be very boring but at least you can get a ton of information about them to remember for future conversations, and you filled that gap of awkwardness with actual talking. Good Job! :P
