Welcome, suadnovic.
Funnily enough, there are guides for that in Finnish, French, Dutch - but not in English. Still on the to-do-list for the admins
But I'll try to help you out in short with the most important things.
- Obviously, have some quality in your uploads. For translation: check on spelling, grammar and punctuation. For the technical part: not too many characters on one line (max 40 is nice, 50 absolute maximum), max two lines, and preferably stay under 25 characters per second.
- Make sure you state the correct and full release name of the video file to which your subtitle is synchronized. Not just the movie name and year or so. This is especially important for manual uploads, because there will be no hashcode.
- Do not delete credits for translation or any editing and corrections. Feel free to add credits for your own work, but leave the original credits untouched.
- Do not upload raw, uncorrected machine translations or duplicates.
Cheers