Preparation and Initial Study
Download or buy a copy of the Morse code alphabet and read it. Put a copy on the wall in your study area and another somewhere else in your house. You need regular practice. Establish a study schedule that allows you sufficient time to relax before studying so you can concentrate on the material. Limit practice and study times to no more than 30 minutes a day, though members of the Radio Telegraph Extremely High Speed Club recommend practicing "a very little at a time" and to "practice little and often." Remember the goal of learning Morse code is to understand sounds as letters, not to read a series of dots and dashes on paper as letters.
Vocalize the Coding
The first step in internalizing the sounds of Morse code is to vocalize the coding as it sounds: say the dots as "Dit," with the "t" largely silent, and the dashes as "DAAH." Read a letter of code aloud to yourself in Morse code while looking at the paper, then cover the paper and say the code aloud again three times. Start by memorizing the easiest letters first: T (single dash), E (single dot), M (two dashes), I (two dots) and so on, according to the number of variety of dots and dashes in the code. Learn letters first, then punctuation, followed by phrases and lastly Q-codes. Repeat this process for each letter until you feel confident of memorization.
Listening and Copying
You may want to start listening to Morse code broadcasts at usual speeds (15wpm) to improve your long-term learning curve; however, if you are looking to learn Morse code sooner rather than later, listening at slower speeds is a good way to master the basics while maintaining confidence. Try the Farnsworth method, which entails listening to individual letters at high speed followed by long pauses to give listeners "thinking time." A variety of free sources of Morse code (or CW) broadcasts are available, the most popular being W1AW, or the American Radio Relay League, which broadcasts a daily Morse code practice text at various speeds.
Establish Proper Practices Early
The dash sound should be three times longer than the dot sound, and the ratios between elements, characters and words need be accurate. Learning at inaccurate ratios will make it very difficult for you to improve your copying speed later on. Ron D'Eau Claire at Elecraft notes that he's "run across many Hams who never learned to copy with the right character and word spacings. ... Because they never learned to copy ... characters at various speeds, they can't copy even if the station slows down." When you are listening, write down each character as you hear it, don't try to read what you are copying and don't worry about characters you have missed; move on to the next character as soon as it starts.
Cautions
One potential drawback of the Farnsworth method of learning Morse code is that it is significantly different from actual Morse code broadcasts, and thus may inhibit long-term development, especially at higher speeds with briefer pauses between characters. Also, when listening, avoid visualizing the dots and dashes; and certainly do not write them down as you listen: this would create an extra step of translation in your brain, and may become a habit slowing you down later.