Here are some resources, mostly written by me, that should be helpful for postgraduate research students. They cover the skills you need to master other than doing the research itself. Some bits are targeted at applied economists, but most of the material is not discipline-specific.
Writing efficiently and correctly
Not by me: Tips on writing well This is not primarily for academic writing, but it is highly relevant anyway.
I recommend that you install Grammarly and use it to check the grammar in all your writing. It’s free.
Grammarly also has a very good grammar guide to help you understand the recommendations that it makes.
Here are a few tips about grammar rules that I find people sometimes get wrong:
On the need for clarity when describing changes in percentage terms
Microsoft Word tips
Publishing in and reviewing for journals
Seminar and conference presentation
Answering questions after a seminar or conference presentation
Communicating with non-researchers
Computer modelling and statistics
The cult of the asterisk (on the need to not apply statistical criteria too mechanistically)
Microsoft Excel tips