I have had my first exposure to English at about six years of age (and have used it ever since), and I generally consider myself a native speaker since I use it a lot (even if this is probably sequential bilingualism at work). All would be fine, if it weren't for those pesky grammar mistakes.
My main problem is that I sometimes make mistakes having to do with the past and future tenses. I simply have no feeling of what's right or wrong at times (e.g should I use "have seen" or "had seen" or simply "seen"). I mostly get it right (I guess, because I have some "feeling" of what I should use). I've recently become interested in correcting those mistakes. Will reading a book (or multiple) help? Can I "fix" this somehow?