Hi hi!
Okay, I hear you, in the same boat about feeling crap about grades!
First of all - can I ask what year you're in? When it comes to late submissions (at least with my uni) depending on how long after the deadline you submit it, they either cap it at 40% (a pass) or fail you.
In terms of tips I can give you to give you a hand with better grades, here's some stuff that I do (I'm in final year)
Prepare a good few weeks before the deadline (if you can)
I always find that I have more motivation at the start of the term. Let's say you get a philosophy assignment about Utilitarianism, for example (I did Philosophy at A Level, hehe) - start your research. Has anyone written a similar paper? Any recent news articles? Can you find any sources that aren't on the research paper?
When citing sources, I'll be honest, I use a website to do all my citations for me. Just Google 'Reference Generator' and you're good to go.
Focus on your writing style
Uni essays are hard when it comes to how you right. Make sure you're not saying 'I' or 'we'; change it for words like 'this essay will' or 'this project'.
Switch up your vocab to - instead of saying 'for example' over and over, maybe say 'for instance', 'for proof'
Re-edit and reread
Keep reading through your essay - is there anything you notice that you maybe do not like in your first draft, or does anything not sound analysed enough. Explain!
Critique
Let's say you find a paper that you like - do other papers exist that discount their arguments? Use it as a way to properly critique it
Peer help
Ask a friend to give it a read!
Try and get it done before the deadline
Leaving stuff to the last minute is soooo stressful. Its so easy to do. Give yourself enough time to try and have it done before the deadline. Then, if you're done a couple of days before it is due, you can sit in bed, with your phone or laptop, and just read it to yourself
YOUVE GOT THIS!!