This page seems a useful flowchart of the process of research, as is this one
This page gives a good outline of methods of data collection
This is a whole website full of research information, including a bizarre rap video about statistics!
There is a lot more to designing a successful piece of research than simply working out the design, and if you're anything like me, then these things will all be much more straightforward. For example:
Sampling - who are you going to use? Where are you going to get them from? How are you going to ensure that they would be an ethical group to use, and how woud you ensure you'd get informed consent from them? Where will the research take place? How are you going to control for age, gender etc? How many participants do you need? What are you inclusion and exclusion criteria? Etc
Measures - what measures are you going to use? Are they reliable for this population? Are measures available or do you need to create new ones? Do you need objective or subjective measures?
Define your research question accurately, make sure you mention that a thorough literature search will be conducted. Is your hypothesis one or two tailed?
Think about ethics in detail - if people are going to be in a control group for an intervention study, how can you justify this? What will you do to compesate people who are not allocated therapy? Are your selection methods ethical, or could anyone feel pressurised into participating? Ensure you get ethical approval before you proceed.
When it comes to the design, think about the stages of the experiment eg. if you're measuring something changing over time, what will you need to measure at the beginning, middle and end? The same things or different things? I think if this is a weak spot for you, be honest about that and explain that you would always consult a book (even state which book or books you'd normally use if you like) or a particular person, for advice and support on this matter. It's important to remember that in 'real life' research, decisions are not made in a vacuum, there is a detailed process of consultation and advice-seeking that means you would never, ever be required to come up with a perfect design, on the spot immediately and go with it. Research is always a process, a process of constant refinement and therefore if you are given a vignette at interview the interviewers will be looking for an awareness of these issues and realities just as much (if not more) than a perfect research design. It was knowing that and believing that that enabled me not only to get through my research interviews, but sail through them. Acknowledging that 'perhaps' I'd do this, but given the time I've had to think about it, I'm not confident it's correct BUT I do know that there are all these other hugely more important things that need to be taken into consideration before I even begin to think about which statistical test I need to use...