Even when invited, don't get in the middle of other people's drama.
Exercise really does make you feel better. It will replace some of your nervous energy with a calm energy. There are gyms where fat people, the elderly and children work out. Seek that sort of environment.
If the primary reason you like that guy is that you sense he likes you, move on. You're better off alone.
You'll never learn how to drive from your friends. Hire a professional instructor. But, whatever, you don't really need to do that for a long time. You built a car-free life for yourself, enjoy it! Driving to work sucks.
You will eventually quit smoking. In the meantime, don't treat cigarettes as a substitute for food.
You'll regret every meanness you remember. Don't be a jerk and don't befriend one, either. Even if that person is smart, charming or funny, you will reach a point where you simply can't stand their company.
You don't have a kid yet (well done and thank goodness!), or anything nearing that level of responsibility. Don't take stuff so seriously, least of all yourself.
The internet is going to be a much bigger part of your daily life than you can imagine, and not just for email. Don't sweat the mechanics, you'll figure it out. What you should know is that it will provide this outlet where you can write the way you write in your journal but other people can read it. And while that sounds terrifying, you'll find this activity both fun and therapeutic. So keep doing what you're doing writing-wise and don't worry that maybe you should be doing something else.