Tear stains are hereditary. The best way to avoid a dog with tear stains is to see the parents and if they have tear stains. They come from tear ducts that are angled incorrectly so the tears drain onto the face instead of into the nasal passage. Tears are clear, but there is a specific yeast that turns orange that feeds off a particular type of bacteria found in tears and saliva. So, it is the yeast that causes the staining in dogs with the bacteria and incorrectly angled tear ducts. Dogs with tear stains will often also have orange stains around the mouth.
People don't want to use angel eyes, but it works. Often you only have to give it for one course of treatment and it kills off the bacteria and doesn't come back, or comes back only occasionally. The yeast dies when there are no bacteria to feed it. Then shave the stains off. You will still get the wet face on and off because that is hereditary, but at least it isn't orange lines. You can also wipe the eyes every day and the tears don't have time for the yeast to grow and stain. Dogs tear more when they have an ear infection (like a fungal ear infection). Get rid of the fungus and the tears mostly stop.
Sometimes the tear ducts are blocked so the tears drain out instead of in. Eye vets can flush the tears ducts, but I have never heard that works all that well. Sometimes dogs with digestive issues like diarrhea or loose stools tear more, too. Pumpkin helps the stools and they tear less.
Some dogs outgrow it. Sometimes dogs tear more if they are sensitive to things like wheat or corn or chicken even. Change their diet and it can get better. It is most common in small poodles. Hardly any standard poodles have it, but I have seen a few.
If you have no ear infections, no eye infections, no diarrhea or any other physical problem, I would try angel eyes once for a couple weeks because often it works and the tears improve or go away and the stains are gone (after you shave them off). But, that's just me.