what preparation should be done to give an interview for managerial post? what questions can we expect from interviewer?

Your level of preparation and interest in the position will be very telling to an interviewer for any management position. First, find out as much as you can regarding the company business, its products/services, its competitors, its current business challenges, its financial position. Do internet research and talk to as many insiders as you can. Second, prepare questions about how your results would be measured in the first 90 days, what significant projects/tasks need to be accomplished in the first 90 days, what is the current caliber of staff reporting to this position, what type of communication is best with the position supervisor, what is a likely path to advancement from this position, why does the interviewer like this company, why do employees stay and why do they leave the company, and more. Great questions to ask can also be found on the internet. Third, you can expect to be asked about significant past accomplishments as a manager, how you get things done, how you give feedback to employees, how you manage time. When speaking of accomplishments plan to be specific about what you did, with whom, were you an individual contributor or team leader/member, what obstacles were overcome, what resources you secured, what results and outcome was realized. Good luck!