Seeing a lot of threads like this as of late.
Here are a few things I've noticed that really seem to help. Keep in mind I'm still new to PBNs. Still testing what's most effective. I don't profess to be an expert. But I feel like people in general have a bad habit of skipping the basics.
1) Age. It seems like age is a commonly neglected factor on BHW. Since our mindsets are based on getting things done quick. But I've been following some competitors in other competitive local niches. A few specifically who are rocketing up the SERPs right not with very few links. These guys are competing against some powerhouse franchise sites. Going through their profiles I'm seeing links on the homepages of PBN sites anywhere between 3-7 years old. I'm also tracking the frequency they're building links and it's like 4-8 links / month max. But these old sites seem to pack A LOT of power.
2) Content. I can't state a direct correlation. All I know is when I first added my links I had like 3-5 pages on my sites. Didn't see much improvement. As time passed by and I added more and more content I noticed my money site increasing rankings. So again, not sure if this was age or Google taking the PBN sites more seriously, but make sure you got decent # of pages on the sites.
3) Recent links to PBNs. Sometimes you buy a PBN site with links 4-5 years old, reregister the site, but the site hasn't gotten any new links in years. So try hitting the sites up with current links. This is something sourcewave talks about quite a bit. Hitting the sites up with socials, web2.0, or other PBN links. Something I'm working on now.
4) Diversify. Don't do 7 PBN links in a row. Do 1 PBN link. Then a few other weaker, highly relevant links. Then another PBN. Mix them up.
5) Relevancy. We all know it's important. How relevant are the links on your PBN, relative to your money site?
-BB