Position is important. Lying on your back increases your chances of tearing. I think standing up does too, but very few women tend to do that....
Intuitive pushing is a big one (not directed pushing). If you push as feels right at the time for you, that decreases your chances of tearing.
Water. Birthing in water decreases your chances of tearing and if you do it's less likely to be a serious one. If you're not in water, warm wet cloths held very gently against you can help soothe and support the tissue as your baby emerges. The wrong kind of pressure can cause tearing inside tho, so need to be careful with that one.
Being numb. If you have an epi effective during the second stage, you can't feel as you push (so you can't push intuitively, see #2, and you are also more likely to be on your back, see #1
). Nit likely if you're at home tho
Episiotomy - if you are cut you are more likely to tear seriously, because cut tissue is not as strong as uncut tisue.
Environment is HUGELY important! If the environment is right, you are more likely to experience a maternal-fetal ejection reflex. This is kind of like your uterus "sneezes" yor baby out of you and they WHOOSH out with very little effort at all; they "free fall" through the birth canal and the "pelvic floor muscles melt away". Ever hear of those women who have 10, 11 lb babies with a super quick birth and the baby comes out really fast with not even a graze? Yeah, that.
Other mammals don't massage their periniums, not even primates with opposable thumbs. But they do tend to birth in certain environments, at certain times. Animals that are normally active in the day tend to give birth at night. Many mammals choose somewhere very private and familiar (except the herd animals that can walk and run very soon after birth). Other animals also don't do directed pushing, because, well, you try telling a cat to pant like a puppy, or a pig to push hard to the count of ten
There may be other factors, too, but these are the first that spring to mind.
JUST my opinion, I reckon staying home and listening to your own body, moving or pushing as iy feels right.... these things will do more to protect your perinium than any amount of massage. All that said, I've never found anything to say that it does any harm... and if it helps you in any way, even if it "only" helps you feel better about your birth.... then that is a good thing