Rituals are a tool for creating a consistent mental state and consequently for creating consistent access to the products of your mind. Classical music is often a good choice for its high replay value. Some also find the music of Ravi Shankar or Philip Glass a good choice. Of course, musical taste is individual. Listen to whatever music which helps you work best, but be open-minded to new kinds of music which may be beneficial.
Some people have a favorite sweater, a pair of slippers, or a hat.
Even Mister Rogers puts on his favorite sweater and shoes before he starts working. Choose clothing which is comfortable. Loose clothing is often best, although at times more formal or constricting attire may evoke a useful sense of discipline and security. Smells can create powerful mental associations, therefore they are useful in ritual. Be proactive about any other needs which might distract you later.