vowels.
You have to be be very careful with vowels in Japanese. If you take an English word like "collect," the stress is on the second syllable: "colLECT." The vowel in the first syllable is a schwa, which is to say it doesn't really matter. It could be any soft vowel. Try it -- say "cillect," "cullect," "callact" or "cellect." They all sound about the same.
But Japanese isn't like this at all. Most of the vowels are soft, and almost always every syllable is important. A word like "nagai" (long) sounds like the stress is on the second syllable. But the first syllable is vital too. "Negai" and "nigai" are also words, meaning wish and bitter, respectively. And context doesn't always help either. One time last year I said to someone after the day's work "kyou wa nagai" (long day today. Actually should have said "kyou wa nagakatta, ne" -- today was long, wasn't it.) But the person I was talking to, heard it as "kyou wa nigai" (today is bitter.)


drinking and second-language ability
Drinking has interesting effects when you try to speak in another language. A little bit really does help -- you struggle less to find the word you need, and you don't think so much about how grammatically correct you're being. But you also make more mistakes. Recently I was at a local tavern, talking to a woman named Yoshiko. It was loud, so we were communicating a fair amount by passing notes to each other. She uses the character for "good" for the "yoshi" part of the name, and the character for "child," as usual, for ko. But some time later I found the notes we had been writing to each other, and looked over them. Instead of writing her name as "good child," I wrote a similar-looking but very different character for "yoshi." So I had written her name as "food child."


collecting
A lot of times I feel like I'm a collector. I might be talking to someone, and catch a word or phrase which I've only studied before. When this happens I feel like a naturalist who's finally seen some scarce species of bird or instinct. So I actually take a picture of that phrase in my mind, and try variations of it when I can. This also makes me realize how important both sides of language are -- both studying it, and using it. I remember reading somewhere, that someone made a study of people who had successfully learned Japanese, and those who didn't. Almost all of the successful ones had studied it for a period of time before coming to Japan. And a lot of people who were not especially successful actually studied it while they were in Japan.