The flute is a great instrument, and many people enjoy playing it. While this short guide will assist you with the basics, actual instruction is the best way to learn.

[edit] Steps

Buy or rent a flute from a music store. When first starting to play an instrument, you should consider renting to be certain that you enjoy it enough to purchase. Also beginners should get a closed-hole student flute. Expensive, professional, open-holed flutes are for more experienced and careful players.
Consider paying a good private lesson flute teacher for lessons. Ask your band director or a music shop employee about it towards the beginning of the school year. This resource will be very useful as you learn to play.
Assemble the flute. Insert the open end of the head joint into the wider end of the body (usually closest to the printed brand name of the instrument). Align the embouchure hole with the first key on the body. Take the foot joint from the case and connect it to the other end of the body. Align the main rod of the foot joint with the last key of the body. Adjust the alignment if needed.
Practice on a bottle to learn how to blow into a flute. Glass or plastic works equally well. Blow across the opening to produce a sound. You should also be blowing slightly downward. The less liquid in the bottle the lower the pitch and the more liquid the higher the pitch. This blowing technique is the proper way to ease notes from a flute.
Try to produce a sound from your flute. Try with the head joint only, at first. Place the lip plate just below your lower lip, purse your lips, take a deep breath, and blow as if you were saying "tooo". It will not happen straight away so be patient. Try moving your embouchure hole around. Practice in front of a mirror and look at the shape of your lips. Your embouchure should be about the size of a drinking straw and shaped like a circle or teardrop.

Here's a neat way to work on producing sound:
1. Press your lips together. Roll the lips inward, so that there is no pink showing.
2. Kiss your flute--place the embouchure hole completely against your pressed lips, so that you can feel the full circle around your mouth.
3. Roll the flute away from your lips approximately 90 degrees, so that the embouchure hole is now level with the ceiling.
4. Pretend to spit out a watermelon seed! This may assist you in finding a good embouchure shape. If you achieve a sound using this method, try adding a stream of air after your initial "spit".
Learn how to hold the flute. Hold the flute with the your mouth on the lip plate and the remainder of the instrument pointing to the right. Your left hand should be nearest the mouthpiece and should be facing towards you from the other side of the flute. Your left thumb should rest on a key. Your right hand should be further down on the flute to the right and should be facing away from you. There is no key for your right thumb. Balance your flute with your thumbs.
This is bad posture; when the flute is held this low it affects tone and breathing.

Have proper posture while playing. Sit or stand up straight and hold the flute a little below parallel. Your arms should feel relaxed, but they may ache after extended playing. Crossing your legs will often affect your tone if you allow you posture to collapse as well. Instead bend a little in the knees to not overstretch them. Keep your head up to allow the air passing through the air channel.
Consult a fingering chart. Many instruction books will have one. The fingering chart will guide you through each note. Try any alternate fingerings. When playing the flute it should not sound like your just blowing or whistling--it should be a full, steady tone.
Warm up before playing. Octave slurs (slurring from the octave below to the octave above and vice versa) are good for flutes. Play a chromatic scale to make sure your flute is functioning properly.
Tune before you play, but after you warm up. Tune to a concert A.^[1] If the tuner says you are sharp (moves to the right), pull out the head joint. If you are flat (tuner will move to the left), push in the head joint. Try tuning to the low and high A. Take into account that cold temperatures will cause an instrument to go flat, and warm temperatures will cause it to be sharp. This is especially important if you are playing in an ensemble.
Buy a beginners book. If you have a band director or a flute teacher they will be able to recommend one. Use your book and try to play some easy music.
Learn how to read sheet music. Most beginners books will start out with the note names on the notes in the staff. However you will have to learn how to read music if you do not know how already.
Become familiar with playing your major, minor, and chromatic scales. These should be printed in your flute book. Music is usually made up of patterns which consist of scales so if you are familiar with your scales you will be better equipped to play the music. Also practice the arpeggios, thirds, fourths, etc. for this purpose.
Clean your flute thoroughly after playing. Use a swab or a cloth strung through your tuning rod to remove spit from the inside of your flute. Occasionally polish it with a cloth.
Take your flute apart and put it away in the case. Twist off the head joint, body, and foot joint gently and put them in the case. Latch the case closed and put it in a safe place, preferably where it will stay at a steady room temperature.

[edit] Video

This video shows the basics of flute playing.

[edit] Tips

Learning to play the flute takes a while. Be patient, keep practicing, and get the assistance of a good teacher. Soon you'll be making music.
Blow into your flute at a slightly higher angle with smaller embouchure hole and faster air to produce higher notes. Play lower notes with a slightly lower angle and larger embouchure hole.
Try rolling the head joint either way to get a better tone.
When learning a piece for the first time, go through the piece without playing and finger instead. Pay attention to STARS --style, tempo, articulation, rhythms, and signatures (key/time). Also watch out for accidentals!
If your flute is consistently out of tune there may be something wrong with its tuning cork. Notice that there is a line around one end of your tuning rod. Twist off the head joint and stick that end into it. When that end is resting against the top of the head joint the line should be exactly in the middle of the embouchure hole. If it is not ask your flute teacher to adjust your tuning cork for you.

[edit] Warnings

Be careful that your fingers do not come very far off the keys while playing. If you try to play faster music this will become a hindrance.
Don't let your right arm droop while playing flute. This eventually causes the rest of your body to collapse and will negatively affect your tone.
Do not grab your flute by the keys. Always lift it up by parts free of any mechanized parts. This will save you from expensive repairs. Do not roll a flute in your lap while sitting either.
Don't drink sugary drinks or eat while playing the flute. Rinse your mouth with water after eating or drinking before you play the flute. It is very expensive to remove gum or candy from a flute.
If you are playing in a warmer area your pitch will tend to go sharp, flat in a colder area. Don't count on this too much (always warm up sufficiently), but if you're playing outside in the cold it's a good idea to push in more than usual.