Should it be within range of your SAT/ACT scores? or lower?
Generally within the top 75% ACT/SAT and an acceptance rate >50%
And you can afford to attend.
Thank you so much 
Ideally, the safety school should have automatic admission criteria that you meet without considering any subjective evaluation (like essays, level of applicant’s interest, etc.) and be comfortably affordable for sure. Of course, it must be a school that you like and has the academic offerings that you want to study.