Two that apply to everyone:
Every bit of your work that can go in a computer should go in a version control system repository.
Everything you do that can be generated on your computer should be stored in a format such that regenerating it from original human-editable sources is as easy as typing "make".
One that applies to everyone who has to write some form of software:
Everything that you write should be accompanied by tests, which should be run regularly, preferably by some "buildbot" system as well as yourself. Otherwise, if you're writing reusable code it's all to easy to break use case A while improving use case B or adding use case C. Even when you're writing use case A, it's easy to trick yourself into thinking the result is more correct than it is unless you've tested it.
There is a world of psychological health in between "This isn't working!?! It was working fine six months ago! I'm screwed!" and "Oops, time to write another test for git bisect to play with. I should probably increase the line thickness in all my thesis' graphs by a smidge while waiting for that to finish."
I don't have time to flesh this out into a full post. Plus, the more material I add the more narrowly focused on applied-mathematics-on-Linux it would get. I hope the abridged version is still helpful.
Every bit of your work that can go in a computer should go in a version control system repository.
For those not aware of it: Google Drive counts as a "version control system" for many document formats. It saves edit histories and allows you to jump back and compare different versions, at least for text documents.
So feel free to use that if it's just for regular writing or essays! (particularly great for essays and papers, because you also gain the ability to painlessly share it and do collaborative reviews and edits, with features to comment on specific parts of the text)
This thread is another experiment roughly in the vein of the Boring Advice Repository and the Solved Problems Repository.
There are some topics I'd like to see more LW posts on, but I feel underqualified to post about them relative to my estimate of the most qualified LWer on the topic. I would guess that I am not the only one. I would further guess that there are some LWers who are really knowledgeable about various topics and might like to write about one of them but are unsure which one to choose.
If my guesses are right, these people should be made aware of each other. In this thread, please comment with a request for a LW post (Discussion or Main) on a particular topic. Please upvote such a comment if you would also like to see such a post, and comment on such a comment if you plan on writing such a post. If you leave a writing-plan comment, please edit it once you actually write the post and link to the post so as to avoid duplication of effort in the future.
Let's see what happens!
Edit: it just occurred to me that it might also be reasonable to comment indicating what topics you'd be interested in writing about and then asking people to tell you which ones they'd like you to write about the most. So try that too!