One of the best things to have contributed to my own RP skills: Reading.
Books are FULL of inspirational material! Whether it be personalities, quirks, or presentation style, I have learned much from simply picking up a good book from a genre I love and just diving in. Basing a character on one you read about can be a great way to get in character. One thing to ask yourself when roleplaying is, "What would my character do?" One subject you might find interesting could be boring for your character, while a subject you detest IRL could intrigue your character.
Sometimes a brainstorming sheet of paper can help.
What are my character's likes/dislikes?
Basic background? Go for something simple, but not cliche.
What fears, if any, does your character have?
What strengths/weaknesses? Are they greedy, yet cautious, for example?
Goals: Money? Becoming an ace pilot? Helping others? Other?
How does your character feel about X group? Studying commonly run-into factions can help with this.
Those are a few things to help you get started. I love books because they sometimes use intricate words that you pick up and learn to use in your own story!
