Any type of instrumentation can be used in a cantata. Start by writing music for an instrument you know you want to include. Even if the first instrument written isn't a main part, it will help get the cantata started. For example, if you know you want to incorporate a piano, a piano rhythm or melody can be the basis of the cantata as a whole. Any instrumentation can start at any time during the cantata piece, lending unique instrumental characteristics that mesh well with other instrumentation or vocal parts.
Vocals can carry the melody or help carry the melody throughout a cantata. Vocals that start at the beginning of a cantata can be any dynamic, depending on what the cantata is about. For example, if you title your cantata "A Quiet Mountain," the beginning vocal dynamic can be soft with vocals that express the image the title presents. If your cantata is titled "The River Screams," for example, an opening vocal dynamic can be loud that captures the idea of a screaming river. If a cantata primarily consists of vocal lines, try writing music around the vocal lines as a way to accompany the vocals.
Creating titles for a cantata should be fun and not forced. Titles can be created as a result of the music written or can be thought of before a piece is written. No matter which method, it is a process that takes time to develop. To keep track of ideas, use a notebook or word processor file on your computer to record the date and any ideas for cantata titles or subjects. Keep a running list in one spot and update frequently so there is an abundant number of ideas to help form the right title.
Depending on the components of your cantata, hold auditions for each instrument and vocal piece. If you are not playing any parts in the piece, it will be necessary to find the right musicians who understand your piece, how each instrumental and vocal lines work together and what the piece is reflecting overall. For example, if you wrote two trombone parts, be sure to address that in trombone auditions and ask the musicians which part they feel more comfortable playing.