Interviews are subjective. The goal of any interview is to evaluate a person on a certain scale. This is not an objective scale, per se where you can score a 10/10 b answering all the questions correctly in a predetermined format. Interviews are different. You need to prepare well for interviews as you can be asked anything. The same theory applies to H4 visa interviews. That said, there is always a way to crack the toughest of interviews, and believe me, H4 visa interview is not that. 
 
There is a predictable line of questioning for H4 visa interviews. Some people are asked a few questions and their H4 visa interview lasts only for a few minutes. Others are asked many questions and a few are asked to send more documents later. Based on my own experience and conversations with friends I am listing few commonly asked questions during the H4 visa interview.
 
1. Questions about You

What is your name?
Where do you live?
What do you do for a living?
Why are you applying for the H4 visa?
Where will you stay in the U.S. once you get the H4 visa?
 
2. Questions about the H4 visa/H1 visa

What is your spouse's name?
When did he get his H1 visa stamped?
What visa are you applying for? Why do you need this visa?
Why do you want to go to the U.S. ?
Why did you not come for H4 visa interview alond with your spouse (that is when he was applying for H1 visa and you did not go for the interview together)
Did you file the visa application or did someone else do it for you?
What do you intend to do in U.S. ? Do you want to work in the U.S. ?
Why was your visa rejected before? (if your H4 visa was rejected before)
Do you have the visa fee receipt?
Do you have your passport/your spouse's passport copy?
Can you show me a copy of his I797 ?
 
3. Questions on the spouse's job & education

What is your spouse's highest degree ?
Where does your spouse work? Tell me more about his company and job profile.
What is his salary? Do you have a copy of his salary slips?
Do you have a copy of his bank returns, recent pay slip and his employment letter?
Do you have any pictures of his workplace (if the name of the company is not known; this question is not likely if your spouse is working for a popular company, say, Facebook, Google, Microsoft, etc.)

4. Questions about your marriage

When did you get married?
Do you have any marriage pictures?
Do you have a marriage certificate?
When did you meet for the first time? (Expect other questions about how the marriage took place)

This is a simple list of questions to give you an idea of what to expect during the H4 visa interview. As I said before it is tough to predict how many questions you would be asked or how long would the interview process last.

Most interviews are easy if you have all the paperwork with you. Be honest. Do not misrepresent facts and you are sure to get the H4 visa. Good luck!