Got firsts in both my pieces of coursework this year thus far.... (72, 78)
Researching a lot helped. Once I had a basic plan from my uni notes, I just googled basic ideas, found good articles, and often they led onto further articles through the references. I had ~100 unique references for my 2000 word essays. Pretty difficult not to be well informed and critical when you've read so much!
Most importantly, actually answering the question properly. I aimed to use words from the Q etc, at the end of each section / point etc, which makes it clear to whoever reads it, and to myself.
Also making sure I had an outline in my intro so I didn't go off course, and removing all non-committal words from conclusions - 'arguably', 'potentially', 'maybe' - even if I wasn't 100% convinced, coming across like you are reads as a much stronger argument.
Also I made sure all my references and points were complete before I started writing - writing is by far the easiest part - it flows much better if you aren't stopping every second to write a reference, and helped reduce errors / poor writing etc. (I use RefME! It's excellent to form references)
And leave lots of time to proof-read - leaving a few days to refresh your mind etc. ie I aim to finish a week before deadlines for this (unlike I'm doing now, oops)
[I mention these tips in particular as they're the main things I did between this and last year - I got 52 and 62 in my cwk units last year to give you an idea of the improvement]