First of all, if you're adding new content, don't worry about getting everything right. We appreciate any effort you make. If you're overwriting someone else's work, though, you should be a little more discerning.
The first priority in an AxTongue translation should be getting someone who does not know the original language to understand it. A clunky translation may be better than smooth one if it provides more insight into how the original line means what it does.
The paired phrasal translations in the subtitles are to work in conjunction with the word-for-word definitions. The best practice is for the definitions to be more literal and the translations to be more idiomatic. The gap between them is often enlightening.
Best practice is for lines to lead with capital letters. Question marks and exclamation points are fine, but periods and commas at the end of a line should usually be left out.
Do not use other people's translations from outside this site without their permission.
You are more than welcome to contribute translations for a language you are not proficient in! Thank you. I recommend using someone else's translation as a reference, in case you miss a nuance. This is not nearly the same thing as copying.
It is often useful to combine multiple words into one bit of text in an original language line, like "ice cream." I recommend splitting all individual words in a translation, but this barely matters.
Definitions should be comprehensible at a glance. One word for one word is ideal. The broader meaning of a term can be drawn out in the subtitles.
If a part of the original language text happens to be in the translated language, which often happens when translating into English, it is better to leave the definition blank than to have the same word twice in the supertitles. You can put a # sign as the definition to prevent this from showing up as a yellow consideration on the right.
In editing mode, by default, "Mimic Mobile" is on. If you have not changed the font sizes, what you see should be precisely what you would see on a device in portrait mode. The best practice is for original language lines to be short enough to fit on a single line, with no line break. The translation can span multiple lines. There are two reasons for this standard. First, the original lines are 2-3 lines in one. Breaking them into 4-6 lines can lead to visual confusion. Second, the longer a line is, the harder it is to parse. It is better to present a learner only a few words at a time. And it is better for learners to start to think in terms of the target language's word order.
Tags are used in two ways: a video's collection of tags determines what videos are most similar to it, and individual tags can be used to construct playlists. Tags are only as good as the videos they match. There is no standard for what the tags should be.
Video titles and artist/source names should be the name that is used for international marketing, if there is one. This usually means they should be in English and in Roman script. Otherwise, they should be in the original language and script. Unlike tags, video titles and artist/source names are shared by all translations. If someone were to translate a French title into Arabic, the Arabic title would show up for every language.