Writing is a part of any honours or PhD project, and it usually models itself on published scientific works like journal articles. Everyone has a different style and approach, but one thing you will always hear from me is to START WRITING EARLY. Beginning researchers almost always assume they should wait until they are done all experiments before beginning writing, but you should start as soon as possible.
This is because writing requires organization to form a narrative. If you don’t have a big-picture view of what you are doing, and why, it is hard to write. But if you don’t have that it is also hard to carry out an experimental study with some self-awareness and structure. As you begin to get results, start writing about the background of the work and how it motivates the need for your efforts. Then summarize your experiments, collecting details while they are fresh. Then summarize your results. Eventually an order will become clear that may not be chronologically how you did the work but best communicates the work done. As you write and work, the writing structure will emerge and will likely help you see anything you may have missed in the lab: extra experiments that prove a point or flawed assumptions, for example.
There are lots of other good principles already nicely summarized by David Weitz in the document: