Stage fright is a challenge a lot of people have. I've acted many times but I still get nervous right before I go on. But once I start performing I totally forget about the people and focus on my character. Focus only on your character and your story. Become that character. If you become the character, then it is this other person up there and not yourself. And don't look at anyone. Pick a point to look at in the back of the room and focus on that. Many performers (including myself) use the nervous energy and put it in your performance: "If you have stage fright, it never goes away. But then I wonder: is the key to that magical performance because of the fear?" ~ Stevie Nicks
Don't feel bad about being nervous. Some very famous people had stage fright: Elvis Presley, Barbra Streisand, Meryl Streep and Sir Laurence Olivier.
Quotes from famous people with stage fright:
"I get stage fright and gremlins in my head saying: 'You're going to forget your lines'." Alan Rickman (Snape of Harry Potter fame)
Tips for memorizing lines
A quick way to learn lines is to record all the lines (and your cue lines) and play them back and say them along with the recording. You can record with your computer, phone, etc. It's important to hear the cue line (line before yours) so you know when to say your line. Play it over and over and say your lines along with the recording. Then when you know it better, pause the recording after the cue line and try to say your line. Listen to the line and see if you got it right and try again.
Other ways that people learn lines include reading the script and covering your lines up. Read the cue line and then try to say your line while it is covered up. Another common way is to have someone read the cue lines and you try to say them. I have even seen people type all their lines as a way to memorize. Look at the cue line and then try typing your line without looking at the script. Everyone memorizes differently so it is good to try different techniques to see what works best.
And right before you perform, you can do a speed through with the other actors. Sit or stand together and go through all the lines as quickly as possible (don't worry about movement). Have someone mark down the lines you miss and read them over and over before you go on.
Advice for teen actors about agents
New actors often ask if they should get an agent.
Don't approach an agent unless you have a lot of acting experience. The best way to get the interest of a good agent is to get a paid acting job (speaking role).
SAG is the best place to look: http://www.sagaftra.org/agency-relations/sag-franchised-agents/sag-franchised-agents
But overall, if the agent requires you to pay money to work with them up front, then it's not a good agent. Good agents only take percentages of your pay when you actually get work.
The exception might be if the agent offers special services such as headshots, website resumes, etc. This should only be optional though. But if they require it, then beware!
If you do not have a degree, consider attending a university such as USC or UCLA to get experience and create networks in LA.
Find more free acting tips at http://www.freedrama.net/acting.html