Here are some of my favorites.
You most likely need a thesaurus, a rudimentary grammar book, and a grip on reality. This latter means: there's no free lunch. Writing is work. It's also gambling. You don't get a pension plan. Other people can help you a bit, but essentially you're on your own. Nobody is making you do this: you chose it, so don't whine.
Do it every day. Make a habit of putting your observations into words and gradually this will become instinct.
Find your best time of the day for writing and write. Don't let anything else interfere. Afterwards it won't matter to you that the kitchen is a mess.
Don't wait for inspiration. Discipline is the key.
The main rule of writing is that if you do it with enough assurance and confidence, you're allowed to do whatever you like. (That may be a rule for life as well as for writing. But it's definitely true for writing.) So write your story as it needs to be written. Write it honestly, and tell it as best you can. I'm not sure that there are any other rules. Not ones that matter.
Read widely and with discrimination. Bad writing is contagious.
Don't just plan to write – write. It is only by writing, not dreaming about it, that we develop our own style.
Open your mind to new experiences, particularly to the study of other people. Nothing that happens to a writer – however happy, however tragic – is ever wasted.
Write. No amount of self-inflicted misery, altered states, black pullovers or being publicly obnoxious will ever add up to your being a writer. Writers write. On you go.
Read. As much as you can. As deeply and widely and nourishingly and irritatingly as you can. And the good things will make you remember them, so you won't need to take notes.
In the planning stage of a book, don't plan the ending. It has to be earned by all that will go before it.
Turn up for work. Discipline allows creative freedom. No discipline equals no freedom.
Be ambitious for the work and not for the reward.
And, this one makes the most sense to me!
My main rule is to say no to things like this, which tempt me away from my proper work.