Firstly, don't badmouth your current or previous employer or coworkers, because doing so could suggest a number of possible negative traits about you, e.g. that you're more inclined to blame others than to reflect on your own shortcomings, you have difficulty working through problems, you talk behind others' backs and/or you're generally a negative person. It doesn't matter whether any of that (or what you said about your employer) is actually true, because the interviewer doesn't have too much to go on and the risk of the above is usually not worth it. That's more than enough of a reason to reject a candidate.
Secondly, don't mention wanting more money, or at least only mention that after you've given other good reasons (and again, don't badmouth your current employer in the process by suggesting that they're stingy or that they're failing as a company). I say you shouldn't mention money because there isn't really anyone would object to more money and employers want employees who care about their job beyond just their paycheck.
Good answers to "why are you looking for a new job" can roughly be broken down into the below categories. As a rule of thumb, I would say anything other than the below would also be a bad answer.
How do you want to grow your career?
This is the go-to aspect you should focus on when answering this question.
Without saying bad things about your current employer, you should explain what your current job is lacking that motivated you to start looking for a job. This is about what you actually do in your job, rather than anything related to the company culture or coworkers. Some questions you could address:
- Which technologies or tools do you want to work with?
- Do you want to transition to a different field or job?
- What skills do you want to learn?
- As a minor point only (again, without badmouthing): Why are you unable to do the above in your current job?
All of these should really relate to the job you're applying for. If you mention things the company has nothing to do with, that's not a good answer.
You should definitely focus a lot more on the positive: things that interest and excite you. Don't focus on things you're disinterested in, because this makes you come across as a pessimist. You could, for example, say something like "At my current job most of my time is spent on X, which [isn't something I'm fond of/I don't mind so much], but I'd really like to focus more on Y; this is something I find fascinating because...".
After you've answered the question, if you have any concerns about whether they'd be able to help you grow your career in the ways you want, you could then potentially ask about that. This would mostly relate to things that would be deal-breakers for you, because it's not going to look good if you ask whether you'd have any opportunity to learn or work with something and they say no. You can ask about less important things less directly at another point in the interview.
The question linked above goes into more detail, but the basic idea is that you should know enough about the culture of the company you're applying to, what they do and the job to be able to convince someone that you want to work there. This is an indication that you'd be committed to the job, and that you'd be happy there, which are things almost all employers want.
"Why are you looking for a new job" is more about your general reasons for looking for a new job (e.g. one of the other approaches mentioned here), so I might suggest starting with those reasons and then adding in how this specific employer seems to meet what you're generally looking for.
If you went with this approach, they may still ask both questions regardless, in which case you should probably reference and briefly reiterate your earlier answer ("like I said earlier", but without being too repetitive) and ideally add a few more reasons why you want to work there.
If you're generally happy where you are, but there's something about this particular company that caught your eye, then you could potentially focus a bit more on this aspect.
What are some deal-breakers or points of concern for you?
Some deal-breakers could be very difficult or impossible to mention without badmouthing your current employer - don't mention those. Others should be easy to mention without making anyone look bad.
This is more of a neutral or slightly negative answer (for the employer) than a positive one, although it could be very useful for filtering out jobs that have this deal-breaker (in that they would either tell you about it, or reject you).
There can be a slight positive here (depending on the deal-breaker mentioned) in that it can demonstrate that you reflect a lot on what you want out of a job, and you're looking for one where you can stay for quite a few years.
You might, for example, mention that your current job involves a lot of travel and you're looking for something where'd you'd spend most of your time at the office. If it's possible or likely that the new job would involve a lot of travel, they're more likely to reject you (which you'd presumably want them to do if you actually don't want to travel often).
Personal reasons
If you are, for example, moving to a new country or city, this might apply. Some reasons may be a bit too personal (and sharing those could very well hurt your chances), so try to use your best judgement here, don't share too many personal details, and rather go with one of the other approaches if unsure. As an example, if you are moving, "I'll be moving to this city on such-and-such date" is about as specific as I would suggest getting. Don't get into your reasons for moving, beyond, perhaps, to reassure them that you'd be staying there for the long term (although it might be a good idea to go into the not-too-personal reasons a bit if the move isn't confirmed yet or you want them to sponsor you, which would be a different question entirely).
If you have such a reason for wanting to change jobs, then you can briefly start with that, and then transition to one or more of the other approaches mentioned here.
Such a reason can potentially count in your favour in that it could suggest you're committed enough to your employer that you wouldn't be changing jobs if it weren't for this unrelated reason. Although it can also potentially count against you in that it could suggest you're a bit desperate (because you must find a new job) and you may not care that much about this specific job you're interviewing for.
For this I would most likely lean a bit more heavily into "why do you want to work here" to counteract the potential downside mentioned above.
