Here are some random little rules that might be useful as you learn Japanese. These were never properly explained in my main book or by my teacher, I found them in other references:
. RU/U verbs: is there a way to determine which is which when a verb ends with RU. I have learned that:
-ARU, -ORU, -URU endings: ALWAYS "U" verb.
-IRU, -ERU: OFTEN (greater %) "RU" verb.
Not necessarily a perfect answer, but it helps with figuring out "U" verbs "on the fly".
. "I" adjectives can usually be converted to adverbs by replacing the last I with KU: OSOI (late) becomes OSOKU.
ex: Osoi desu (it's late) vs. osoku nomimasu (drinking late)
. "nani" becomes "nan" in before d, t and n.