Well, one of the reasons why I always say I don't speak Spanish (even if I've been posting a lot in the Spanish forum) is that, except for basic constructions and vocabulary, I mostly just transfer from Portuguese to Spanish. Sure, the languages are close enough for it to work quite a lot (it'd be a disaster to do it in Italian, for instance), but yet... I can already see myself doing the very same thing with Japanese and Korean (and that could be quite more complicated, hehe).

However, I also force myself to think in the language I'm studying, even if in a basic level. When I'm writing in Bulgarian, for instance, I'll look up a verb in the dictionary, but will then conjugate it in my head, and think of complements it may take in Bulgarian, too, instead of thinking of how the verb would work in Portuguese or English.

I agree that expressions are the worst part when you're trying to learn a language. Take German for example; apart from its hellish counter-intuitive grammar and strange vocabulary, it's also loaded with expressions completely different from the equivalents in English. Whereas English prefers verb phrases, German uses noun phrases more frequently. Gah.