The first rule: don't start with rules!

Don't go by a rule book.When learning a language, don’t accumulate rules in your head. 

Now, I realize that this advice is wildly counter-intuitive. But consider.

Every rule that you learn is just one more thing to remember. The more of them that you learn, the greater is the chance that you forget them.

And even if you never forgot a single rule, do you think you’d ever learn all of them? No one has, even the top linguist ever. There's no end to them. They are continually being discovered.

But the worst thing about rules is that they clog up your mind. They are worse than cholesterol on the brain. Every extra rule demands a larger and larger lexicon of material to refer to before you open your mouth or touch a keypad.

They inhibit you from using the language. You ask yourself: Is this right? Is that wrong? Is this an exception to the rule? Does this application of the rule conflict with another rule?

Final point: How many rules do you know and think about when you use your own language? None, right? 

Do you ever stop to think about when to use the article 'the'? You know that there are about 63 rules just about that word alone, didn't you?

Internal grammar and spelling

Internalize the grammar and the spelling too.

It’s a fallacy to believe that you can learn a language by studying its grammar. And to a great extent the same applies to spelling, despite the fact that schools try to teach you with spelling lists and spelling rules.

The truth of the matter is that you mostly just develop a sense what looks and feels ‘right’. This happens when you see the same forms again and again. You get used to seeing words spelled in a certain way, and words arranged in certain orders. (People who read and grade papers with a lot of mistakes find that they begin to lose that sense!)

The thing then is to get a lot of exposure to the language that you want to learn. Automatically you pick up grammar and spelling along the way. There may be a few gaps left over, but you may learn them as exceptions. It’s not the rule to learn the bulk in this way.

Even if you could learn all of the rules—quite impossible, as no one has ever managed it!—it wouldn’t do you any good, as you wouldn’t be able to retrieve and apply them rapidly enough for even ordinary conversation and texting.

Grammar sucks

Somewhere along the line, people got the idea that the way to learn another language is to study its grammar, and then to practice applying those rules, translating from one language into the other. That's the  'Grammar Translation Method'.

It is derived from the 'traditional' or 'classical' way of teaching Greek and Latin. Well, you know how useful that was for your schoolboy Latin!

Intuitively, grammar translation seems to be the way you'd go about learning another language. Trouble is, it doesn't work. Or rather, it does work (because every method will eventually get you there) but slowly, painfully, boringly, and tediously.

The Grammar Translation Method has been deemed ineffective by the authorities themselves.

We don't even get taught the grammar of our own language at school anymore for that very reason.

How can I get across that point most succinctly and forcefully?

How about this: no one out of all the billions of people in the world ever ,earned their own language through studying its grammar. Not one. And yet 99% of people could use their mother tongue within a year or two of birth!

The grammar of a language is NOT the language itself. They are two totally different subjects. No one confuses Physics with Physical Education.