The following is for right-handed players. Reverse "left" and "right" if you're left-handed:
The classic way to hold the guitar when playing flamenco music is to sit with your left knee a little higher than the right. Set the curve of the guitar on the left leg. Your right hand lays across the larger part of the body of the instrument, thumb resting on the top string, pinkie finger on the bottom string.
A major difference between flamenco and the usual plucking or strumming you see modern guitar players do is the lack of a pick or plectrum to rake across the strings. Accomplished flamenco players usually have long fingernails on their right hands, and they use those fingernails to pluck the strings with an upward motion. The thumb, however, moves in a downward motion.
When plucking the strings, try to move only the fingers that are being used. This will keep your hand in the correct relative position on the body of the guitar and make it easier to strike the strings you want.
Practice using your thumb to pluck the biggest string (the low E or sixth string). Pluck the fourth string with your index finger. Pluck the third string with the middle finger. Use your ring finger on the second string and the pinkie finger on the first string.
Now drop the thumb to the fifth string and pluck it. Repeat the exercise, using the rest of the fingers on the strings, in order. Vary the exercise by holding different chords with your left hand.
As in all forms of guitar-playing, the most important thing is learning the chords, especially major and minor, and memorizing each note on the guitar neck. Practice with sets of chords until they become second nature to you. Gradually add more chords that fit the type of songs you want to learn.
For your right hand, a good flamenco exercise is to make a fist by closing, in turn, the little finger, ring finger, middle finger, index finger and thumb. Then open the hand, using the same order of fingers. Then do the same exercise in reverse. That is, close the thumb first and the little finger last. Do these right-hand exercises up and down against your guitar strings until you develop a smooth, easy stroke that causes your fingers to brush along all of the strings. If you don't have your guitar handy, use your side, a leg, an arm or a book to practice.