Any tips from people who's letter got through?

Hello!

My first letter got RTS after 2 months (I sent it from Europe) and I'm trying to figure out why. The adress was correct and the envelope even got opened. The only possible reasons so far include: my address (in the top left corner) got lightly crossed out by a postal worker here in Austria because it's standard procedure when sending a letter abroad, the text in the letter didn't have any margins and I didn't write my name in print beneath the signature nor did I write the date anywhere. To anyone who's letter got accepted: did you send it with tracking/priority? Was the paper clean or lined? Did you leave room for margins, etc.?