Get a grasp on music notation and how to read it before you begin your interval ear training. Knowing what a minor third sounds like is one thing, but being able to write it down clearly for any musician to see and read is another. The next basic needed is a general understanding of the piano keyboard. Ear training requires repetition and practice. When training your ears it is important to be able to read the interval and then play it on the piano so that you have the aural association.
Musicians are mnemonic learners, and any little trick can help. Use a variety of sound and song associations to your advantage. For example, the theme from the movie "Jaws" is nothing more than a minor second interval. A tritone is the opening interval in "The Simpsons" theme song. Every interval has been used in a familiar piece of music. These pieces can help you quickly identify the intervals. Song association is a popular form of ear training for beginners.
Solfege is a technique that helps you improve your sight singing ability and general musical knowledge. Solfege associates musical syllables with pitches instead of note names like A or C. The basic solfege scale is Do Re Mi Fa Sol La Ti Do. If you are training yourself to hear a perfect fourth, you could think about the opening of "Here Comes the Bride," or you could think of the solfege, Do to Fa. Enhance basic solfege skills by singing scales.
The easiest way to practice is to use an online trainer. These trainers play the audio clip of an interval and score your progress as you identify it. This will give you an idea of your strengths and weaknesses and can help you track your learning progress. Another practice asset is the piano. Using the piano will allow you to hear, feel and see the intervals directly. However, it may make it more difficult to test your progress.
Advanced techniques of ear training include exercises such as sight singing and melodic dictation. Sight singing involves taking a piece of music and singing it without ever hearing it, just basing the performance on the intervals that are written on the page. This is a method in which notation skills come in handy and can be attempted with any piece of sheet music to an unfamiliar tune that you have never seen before. Melodic dictation involves hearing a song or musical pattern and writing it down note by note based on the pitches and intervals you hear. It is helpful to reference the actual sheet music to check your dictation once you complete the exercise.