Teach yourself all of the basics of clarinet theory. If you are going to play in unison with another clarinet player, you must first know all of the basics of clarinet theory for playing alone. A good way to do this is to sign up for lessons if you have not done so. That way a professional clarinet instructor will teach you all of the basic techniques and theories of clarinet playing.
Practice alone frequently. Continue to practice everyday for at least one hour. Every time you play, you will learn something new. By practicing frequently and reading music, you will begin to develop your skills day by day. Reading music will also allow you to understand scales and how different chords work together to form a song, which is an essential part of playing in unison.
Select a song to learn to play in unison with a friend who is equally as skilled at clarinet as you. Start by focusing on mastering only one song before you and your friend move on to other songs and more difficult pieces. Once you select a piece, purchase the clarinet and piano music for the song.
Go over the music with your friend studying the chord by chord structure of the song. Piano music is important when starting to play in unison because it has already done the work for you. Unlike clarinet music, piano music is written with a treble and bass clef that are meant to be played together to create harmony.
Select whether you will play the bass or treble clef. Your friend can play the other. When you play each clef together, you will play the song in unison. Timing and practice are key, so continue practicing until you both master the piece. Once you have done this, you will be able to move onto other pieces and eventually will not need the piano music since you will know which chords play in unison together.