This is also my weakness. Sometimes my fellow language-learners would ask me "Do you use American spelling or British spelling?" and I answered, "I don't know. I just rely on Microsoft Word about my spelling choice. If it shows a red underline, I change to the other option". Pronunciation is also my other weakness.
As for my strength, even though I have bad memory but somehow I can memorize vocabularies rather easily. Also, since my main "weapon" is math, I can see grammar patterns as algebraic expressions, really saving my time of understanding things.