As a post doctoral researcher, you can be hired on a project for 1 or 2 years, on a topic that is different from the topic you worked on during your PhD years. It may feel daunting to start all over again, and do it in less than half of the time you needed to do your PhD. As I've worked on a number of different topics during my post-doc years in Delft (including my "new" research line on load testing), I'm here to demystify the process.
First of all: remember that you are trained to do research. Your PhD years were the years in which you learned how to do research. Writing your dissertation and/or first journal articles were the training you needed to grapple with your writing style, find your identity as a scholar through writing, and learn the ropes.
Does that mean that when you start a post-doc, you can make a plan from start to finish of the post-doc project and simply execute? No - research is never a straight line. You will get stuck, you will struggle with your scholarly identity in writing about a new topic, and you will have to start again when something doesn't lead you to discovery. Just as for the PhD trajectory, it is difficult to plan a research project - but allowing for plenty of buffer time in your planning and having an overall idea of what is expected from you, should help you draw a blueprint for your planning.
Since the general steps of a post-doc project are similar to a PhD trajectory, I will here discuss the particularities only of a post-doc project.
1. Topic description
A post-doc project usually comes with a more specific description that a PhD research project, since for the PhD it is expected from the candidate that he/she comes up with a significant novel contribution. This contribution is often required to be in the form of a new theory - and many supervisors will leave it open to the candidate to see how he/she will develop such a theory.
For a post-doc project, there is often a more specific description of the problem, as well as of the expected deliverables and their deadlines. The topic description is a good starting point to define your research question for the post-doc project.
2. Literature review
A post-doc project doesn't give you the time to spend a year exploring the literature, as you may have done during your PhD years. You'll need to be able to set up the literature review in a reasonable amount of time. If the post-doc project is part of a larger research project, you can collaborate with the other researchers (post-doc and/or PhD) to develop your literature review. If not, you can take the topic description as a starting point (this description will typically have literature references that can help to get you started).
As a post-doc with a limited amount of time, you need to delve into the literature with a purpose. While I generally encourage reading broadly for your general interest, you won't be able to read and reread all interesting articles on your topic and then decide what you want to do with these. You will need to start turning the literature directly into elements for your deliverables. If you need to study a new theory, take the seminal papers on the topic, and work your way through these by taking plenty of notes and/or deriving the formulas yourself. Document this work in a background document for yourself. If you'll need the formulas later, program them in a spreadsheet. If you need to set up a database of experiments, start developing this database while you read the articles - don't make the mistake of reading all the articles first, and then processing the information. Similarly, start drafting your literature review report right as you are reading the articles. Take screenshots of interesting information, type discussions of what you read, and place this information within a report that has an outline which you can either shape as you read or set up from the beginning.
During your PhD years, you may have been able to devote 80% or more of your time to your research project. As a post-doc, you can be balancing your new research project with writing papers about your dissertation, taking on service appointments, supervising students, and perhaps you help with some of the teaching in your department. Planning is more important than ever. If you need to balance a number of responsibilities, try out using a weekly template.
Your long-term planning should focus on the deliverables of your project - make sure you plan towards them and leave plenty of time for dealing with setbacks in your research.
As I mentioned earlier, research doesn't become "easier" as you move through your research career. The very essence of research is dealing with the unknown, so just as during your PhD trajectory, you will iterate towards a solution. You may be expected to handle the same amount of experimental data as during your PhD in a shorter amount of time. If you have a number of responsibilities, make sure you can carve out the time you need to think and do deep work. Your PhD credentials already show that you can do research - now make sure you make the time and have the headspace to crunch numbers and do the work.
5. Publications and deliverables
Post-doc projects typically require you to submit a certain amount of reports to the funding body, or submit a certain amount of papers for review by a certain date. Besides the publications from this project, your post-doc years also can be the right time to turn your thesis into journal articles. Make sure you put writing on your calendar to move your publications forward - these are incredibly important for your future career.