Pre-transition, I tended to wear Asian-style embroidered jeans, fairly tight-fit V-neck t-shirts, a slim-fit jacket, and plain converse shoes. I wore a silver ring on my right hand, a unisex necklace, my hair to my jawline and curled around my ears, and I was clean-shaven (and I never had enough for a visible shadow). The result was I was seen as an androgynous girl about 15% of the time, and a femme-y gay boy the rest.
But it all depends on what you start with. I was slight, physically androgynous and with a voice that could rarely pass as male. If I'd styled my hair and plucked my eyebrows, I would have passed as a girl most of the time. If I'd switched to female clothing and used face paint...
It's much harder to do that kind of stuff if you have distinctly masculine facial and body features. The closer you are to the "baseline" pre-puberty model, the easier it is to slide back and forth in peoples' perceptions.
But I would get a gender-neutral hairstyle and pluck your eyebrows the way Smooth recommends, find the least genderable clothing you can for your body-type (tighter is better if you are slim), alter your body-type if you feel comfortable doing that and aren't already in the low fat/low muscle category, and start working on moving your voice into the andro-range 140-170 Hz, removing chest resonance, and changing your intonation. Then see where you are.
I'd also note that andro presentations draw attention. No people won't generally care, but they will LOOK - particularly if you are conventionally attractive. And for someone who previously presented as an ordinary guy, you will notice a difference.
