The quality of being elusive is possibly elusive in and of itself but with a little practice you might be able to perfect it.

1. Always leave an air of mystery about who you are. Don't tell everyone everything about yourself; leave plenty of things for them to guess but don't provide confirmation of their guesses.
2. Don't answer all the time. When the door knocks, don't answer it. If you live with other people, tell them to answer it and let them know that you're "not at home". Don't answer the phone; make people leave messages which you can choose to answer or not in your own time. Don't tell people where you live - let them guess but again, don't confirm it.
3. Never commit to anything unless you absolutely have to. Instead, leave a sense of possibility at your involvement but it's entirely up to you whether or not you'll get involved. Turn up to events or occasions sometimes but not other times; but never directly answer invites or requests. Say things like: "Maybe I'll come, I just know yet.", "Perhaps I could make it but there is not certainty.", "If I'm in town I'll try to come." and leave it at those vague statements.
4. Never reveal your favorite brands, scent, TV shows, etc. Again, leave people guessing. If they ask, hedge your responses with vague comments such as, "It's always changing, so I don't really know right now.", "Well, I used to like a certain brand but it went out of production, so now I'm still looking for a replacement as good as it was."
5. Avoid participating in school or community projects on a regular basis. Turn up now and then to offer occasional help when people least expect it but most need it. This will develop a pattern of them understanding that you're worth knowing and having around but that it can never be certain when you will be.
6. Have a wide circle of friends+. See different friends all the time and don't make really close friendships unless you know that you can trust them to respect your need for being elusive. If there is any sign that they find you unpredictable in a negative way, make it clear to them that you never promised to be a reliable sidekick.