Skyforth is a very valuable item in Path of Exile, and they are the best boots for very many powerful builds that are very popular. So if you are playing one of these, you definitely want a pair of Skyforth, but getting them is pretty difficult.
If you can afford to, buying a Skyforth is the best and most reliable option. Other than that, finding white Sorcerer Boots that you use Orb of Chance on is a good strategy. These have a very small chance to be upgraded into Skyforth, so it is well worth it to pick up and upgrade all of these. You need a pretty good amount of luck to get a pair, but enough boots and Orbs of Chances will get you one.
It is also possible to use Orb of Chance + Orb of Scouring on a pair of white Sorcerer Boots until you get the Skyforth boots. You will on average need a whole lot of boots to pull this off, but after enough orbs you will get the boots.
Skyforth can also randomly drop from any high-level mobs, but the area needs to be level 82+. They will be found as Unique Sorcerer Boots, so pick up these!