On self-awareness Your sense of self has to be constantly maintained. It feels like a natural ability to be self-aware, and perhaps it is. Perhaps it can't be taught. However, it can be practiced, and it can be exercised. You know this because of this very practice—journaling is a way to observe yourself and keep yourself on the right track when you've fallen off. If you're willing to critically and objectively observe yourself, you can improve for next time.
On being self-centered You seriously spend way too much time talking about yourself. This might be a sign of a bigger issue, too. It seems like you even get bored with other people because they're just not interesting enough in conversation. As if it's a competition to see who can be the most interesting. Is that a competition worth competing in? You're insignificant in the grand scheme, and acting like you're not for a short period of time does nothing to change that. Never make declarations about yourself or proclaim who you are. Always demonstrate it by your actions, not your words. The people around you should comment on how much you yield to others, not how much you own a room. By letting everyone else speak about themselves and paying close attention to what they say, you'll truly own the room. You'll be able to connect with them better because you took the time to understand them rather than make your own assumptions and force yourself to operate accordingly. Ask more questions. Be more curious.
On the vanity of "yes" Saying yes or even hesitating to say no to people is pure vanity. You're not a nice person because you constantly say yes to everyone, you're just vain. You want them to like you, and that's why you say yes. So, what? It is difficult to tell people that you have to go because you only have 24 hours in a day and they aren't the number one priority for most of it. It has to be done! The people and opportunities you say no to are not bad, either. They're simply not where you should be spending your time in a given moment. Don't become so vain as to bend at the whims of everyone around you. Please your God and yourself, in that order. If a person isn't a part of that plan, then say no. Say it respectfully and allow them their dignity, but say no. You're not doing yourself any favors otherwise.