Start by deciding what clef you will use. The treble clef is used for most vocal melodies, the right hand on the piano, and instruments such as the violin and flute; it is the most common and the first clef most musicians learn. The lines of a staff in treble clef from bottom to top are E-G-B-D-F: think "Empty Garbage Before Dad Flips!" (Or make up your own!) The spaces, bottom to top, spell FACE. Use these memory tools to practice placing the notes on the staff.
Use bass clef for the left hand of the piano, very low voices, and instruments such as bass guitar and upright bass (notice a pattern yet?). The lines of bass clef, bottom to top, are G-B-D-F-A ("Good Boys Deserve Fudge Always"); the spaces spell "All Cows Eat Grass" (A-C-E-G). Memorize the positions of the notes in bass clef, or keep a cheat sheet nearby until you do, and you will know where to put any note on the staff.
Remember that there are notes in between the staffs, too. To find these notes, simply continue the musical alphabet, A through G, on each line and space. In this picture, the note on the left is D, and the note on the right is Middle C. Below it there is one more note, B, before the bass clef appears.
Begin by drawing the note head on the line or space where it belongs. For example, start with an E in treble clef. (You may have noticed there are two E's, one on the lowest line and one on the highest space. They are an octave apart, so choose whether you want a high E or a middle-range E (lower E's are in the bass clef). Let's go with Middle E. Middle E's "note head" will be a circle on the lowest line of the treble clef. The staff line should bisect the note evenly, dividing it in half, so it is clear exactly where the note falls.
Now, draw the stem. Follow this rule of thumb: The stem of any note on the lower half of the staff (in either clef) will go up; the stem of any note on the upper half will go down. (B's stem can go either way.) Middle E's stem, then, will go up. Place your pencil on the right side of the note head, and draw a straight line, about halfway up the staff.
Say our next note in the melody is a C. Find C on the staff and draw a circle in the space, close to but not touching, the adjacent E. This placement indicates that the C comes after the E; if you want the performer to play them simultaneously, place the C directly over the E, and draw both stems in the same direction---in this case, with a note on the lower half and a note on the upper half, either way is acceptable. Notes in the spaces of the staff, such as C, should touch but not cross the lines above and below it.
Make a grand staff if both right and left hands are playing together (or that more than one instrument or voice is playing). To do this, draw the bass clef on the staff immediately below the staff with the treble clef, and connect the two staffs with a vertical line, as seen in the picture. On the grand staff, continue writing in notes as normal, making sure to line up vertically notes that are played together. If you are only writing a melody, then don't worry about a grand staff.
Notice how in the examples for Steps 3 and 4, several different kinds of notes are represented. The notes drawn on the treble clef in Step 3 are called half notes; they generally last two beats. Those drawn in Step 4 that are attached by a double line are sixteenth notes. Quarter notes (the first note in the treble clef of Step 4) last one beat in most musical scores, and they can be identified by their filled-in note heads.
Learn the different kinds of notes, as seen in the picture. From left to right, you see a whole note (4 beats), half note (2 beats), quarter note (1 beat), eighth note (half beat), and sixteenth note (quarter beat).
Practice drawing the various kinds of notes so that you can use them to more accurately reflect your music on a page. The more you practice hearing and writing pitch, intervals and rhythm, the more sensitive your ear will be, and the easier writing musical notation will be.