You're in luck - female bodies can pass for male often without too much difficulty. If you haven't much arm hair, a jacket is probably advisable (which will also deal with slenderness).
Mostly it's about presentation I think. If you make a vague attempt to cover up feminine features, people will make assumptions from your clothes. I strongly suggest cutting your hair if you are considering doing this long-term. Assumptions are made a lot from hair length.
For the record, I'm a post-op almost 20 year old Female-to-Male transsexual, so I have been on the road for quite some time and would be able to answer specific questions about what I have found useful/not useful in passing. Although of course, I don't know what your purpose for cross-dressing is, so unsure how appropriate my experiences are to your situation.
Last edited by lightburns; 18-04-2012 at 17:02.