Suzuki piano accompaniments almost always include a one- or two-measure introduction. Practice counting this introductory window so you can cue and enter confidently.
You can find the Suzuki Viola Book 1 Piano Accompaniment PDF online, but be sure to verify the authenticity and legitimacy of the source. Some popular online resources include:
Beyond legality, there are practical reasons to avoid bootleg PDFs of the "126" accompaniment: