Here is a brief guide to tackling them when you are horribly stuck:
1. Submit it. Even if it is the most terrible, horrendous, rambling shit in the world, submit it. You will definitely get 0 if you submit nothing, but you might get more than you think if you submit something. If your module has substitution applied, then so much the better, but something is better than nothing.
2. Read the question. This sounds so obvious, but many's the time I've skimmed the question, and think I've got it, only to realise I've missed two tiny vital words like "two sources" or "after 1800". So read it, and grasp what you're being asked even before you do the reading.
3. Read the guidance. Unless you're in an exam, the guidance tells you pretty much exactly what you're being asked, where to find the information and how to write it. Got to write a report and you've never done one before? Guidance! Source analysis? Guidance! The guidance will also tell you things like whether you need to include references (almost always yes, but check anyway), or diagrams.
4. Gather up your materials. There is nothing worse than being halfway through answering a question, realising you've left the relevant information upstairs, going to get it and then utterly going blank when you sit back down. The guidance should tell you what you need, as should your own common sense.
5. Answer the question. The way I approach TMAs is to read the question, and then give a short answer in my head. "Did the introduction of the Whatever Act of 2000 change things?" it might ask, to which I say "NO!" And then I have to decide why I've said no, and that's the basis of the essay. Tie every single point you make to the question.
6. Obey the word count. The word count is not an arbitrary sum the course writers have put in to annoy you; it's a very important clue to what to write. Give 10% of your word count to both your intro and conclusion. What's left is enough to cover everything. If you massively exceed it, you're either waffling, repeating yourself or going off on a tangent. If you come massively under, you're missing something.
7. Edit with extreme prejudice. If you can't bring yourself to, get someone to read through it and point out repetition, spelling mistakes and lost threads of argument. Leave it a few days, unless it's very last minute, so you're looking at it with fresh eyes.
8. Reference as you go along. I wrote a guide to referencing here, and do not understand why you would EVER wait to the end of an essay to reference it.
9. This is very basic, but check your full name, personal identifying number,the course code and TMA number are on every page. I set up TMA answer sheets at the beginning of the year and stick all identifying information in a header, and then never worry about it again.
10. Know when to stop. If it is 11:55pm on deadline day, and you're still staring at it blankly, hoping for errors to jump out, stop. If you are convinced you're going to fail and you haven't submitted because you're hoping for inspiration, stop. Submit it. Be kind to yourself. IF you get so it's two days before submission and something horrible happens, don't be afraid to ask your tutor for an extension. Just make sure you submit something before the extension expires.
11. SUBMIT! DO NOT FORGET TO SUBMIT! Check your deadlines, write them down EVERYWHERE, and do not forget to submit!
12. Relax. Even if you're so behind it makes you want to weep, and your next TMA is due two hours later. Give yourself a pat on the back, and a small treat (mine is usually a day stuck in a book unrelated to biology or medical history).