Update: "to appreciate" has multiple meanings, I'm specifically interested in the one that expresses gratefulness; quoting Wiktionary:
To be grateful or thankful for.
Some relevant translation of "appreciate" I've found are "<etw. Akk> schätzen", "sich <etw. Gen> bewusst sein", "für <etw. Akk> dankbar sein" and the phrase "sehr nett von Ihnen/dir".
What construct can be used where I would say "I appreciate it" to emphasize that I'm especially thankful for a favour in English? I'm interested in both an informal situation ("I appreciate you walking the dog this morning, honey") and in a formal setting ("I appreciate you preparing the documents in advance to speed up the negotiations").