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.