Humor always helped me. If I needed to remember a sentence construction, I would make up a silly sentence using it (even though it often meant learning unnecessary vocabulary words) and it generally helped me remember. So even now, 14 years after I took my last Russian class, I can still remember how to say "Pardon me, do you have any Grey Poupon?" - which happens to have an important sentence construction for conversation.

I took one semester of Italian for fun with one of my best friends, and we would either make up parody versions of stuff we needed to know (an example would be substituting "Scramuzza," the last name of a mutual acquaintance, for "scusi") or making up joke sentences.

The other thing is, as far as accents are concerned - it sounds lame, but I found that if I tried for a completely fake and cliche accent, it actually sounded pretty good when speaking the actual language. It worked for me in French, Russian, and Italian - I ALWAYS got high marks for accent and pronunciation, when I was just channeling bad movie accents. It didn't work so well for Chinese, though, and Japanese accent was more a matter of speaking with the right parts of the mouth. (The only one of these languages I'm even marginally fluent in now is Japanese, mind you.)