Answer:
"Effeminate" is a cultural term. Certain behaviors are typical of women, others of men. Obviously, playing up these stereotypes is sexist, but basically that's what you're after. So the easiest way is to observe women and copy some of their mannerisms.
A few suggestions: In our culture, certain walks are considered effeminate -- women move from the hips, men from the abdomen or chest. Men tend to make abrupt, linear gestures. Women tend to make even, curving gestures. Women handle most things -- dishes, even furniture -- as if it's very fragile; men just grab it. Women tend to pay more attention to their "image" when they stand or sit, and may arrange their clothes to be more flattering -- men just sit down and stand up.
The trick with all of these behaviors is to do what actors call "internalizing" them. That means they have to seem to come from inside of you, not like you're imitating someone else. So practice!