By saying affirmations in the mirror can help. Say these with assurance, that you mean what you are saying. Act like you are a teacher and not the student, even though you are in training.
Say things Like " God loves me, Jesus loves me, I know who I am and I am one of God's best creations, I am uniquely made, I am wonderfully made, I'm sure that God loves me, I am exactly the way I am suppose to be, I was made in the image of God, I am a creator too, I have full assurance in my life".
"God has my back, Anything I need to know God will give me the answer". "I am confident, I am sure of myself, I am blessed to be a blessing, I make good things happen, I make a difference, I am making a difference today, I am blessed by the best, God is love and God loves me, I am not subject to fear in Jesus name, I am subject to be blessed and to be a blessing, etc.
Keep up your appearance, make sure you look your best, shine your shoes, speak with authority but be respectful and friendly. Let your actions say you know what you are doing. Give someone a smile once and a while, be a blessing and help someone else who needs a hand.
For a relationship say " I am sexy, I am fine, I am not egotistical but I am not lame either. I know I can do anything I set my mind to".
Keep active in telling yourself in the mirror or record yourself on a MP3 player by affirming positive quotes. Listen to them in your head phones for at least 30 minutes a day everyday. And when you say it you have to sound as sure as possible when you say it or record it. Otherwise it will not work. Be yourself but just be all you can be this time. Believe in yourself and speak yourself into a new you. Hang around confident people. Watch and learn from them. How they are cool, in control and relaxed. Begin to tell yourself after some time "this is easy, I can't lose, I got this".
Please read my other hubs on Relationships, etc.
Hope this helps :)