Common Mistakes
 

I thought it might be a good idea to point out some common mistakes that foreigners make when speaking or writing Japanese to help everyone not make those mistakes themselves.

An example would be something like:

一番友達 when it should really be 一番いい友達 (いちばんいいともだち) because 一番 cannot directly modify a noun.

Because I'm not Japanese I'm not sure of many more examples of common mistakes (I'm sure I make them all the time though) besides just mixing up particles like で and に but I would be happy to learn of other ones so maybe I can avoid them =)

Common mistake for beginners is they use わ instead of は when typing the particle. For example, 'watashi wa' is '私は.’

I've done a lot of mistakes when writing myself, but I can't recall exactly what they were. I'll put more as I learn more~

Says who?

一番星= the first star of evening
一番ホーム= Track #1 (at a train station)
一番打者= the leadoff batter (in baseball)
一番茶=　the first picking of tea
一番弟子= one's best pupil

and the list can go on......

Confusing "i" adjectives with "na" adjectives

たのしい - たのしかった

Where as people just slap "deshita" on everything.

Using pronouns just like you would in English, and when people use の? on the end of sentences to denote a question they always forget the to say なの? instead for nouns and な adjectives.

I figured that was going to happen. Just another common mistake, I guess =)

Would it be accurate to say that it must modify an adjective or adverb when referring to your "favorite ..."?

Yes, it would.

I must add this time, though, that your example "一番いい友達" is grammatically perfect but you won't hear us native speakers say it that way very often. We would say it:

一番の友達
一番好きな友達
大親友

昨日は寒かったです。
often gets written as
昨日は寒いでした。

I had no idea, thanks =)

Though in colloquial Japanese you will hear young Japanese play with these い and な adjectives. きれい is a な adjective, but I hear people say きれかった meaning "It was pretty" instead of きれいだった.

But your opposite example is never cool.