How do I improve my social skills?

Lately I have noticed my social skills have gotten really bad, I mean when I look back at school, I said to one of my teacher's "good morning, Mr. Jameson" and he replied with "Shut-up." I then tried talking to a girl, I said "Hi." she replied with hi, I then said "How are you doing today?" and she walked away and ignored me. I think the brain injury made me this way, nobody would talk to me, I tried talking to Darren and he said "Go away man, nobody wants you here." I just said to him "Um excuse me, do you know where room 101 is." I then tried talking to Alyssa I said "Hi." she replied with "hi." "About James." "Do you mean my boyfriend." I replied with "Yeah he's a real jerk, he broke into your locker (in which he did) and took all your stuff." "Oh really, am I really supposed to believe this crap, go away." "Alyssa." "Holy sh*t dude shut up." I feel horrible, how can I improve my social skills so I get my message across better and could someone tell me what I am doing wrong in each situation.