- High-conviction, Margin-of-safety and size of gain (given opportunity cost), roughly in that order. You need to pick winners where you can bet big enough to make substantial gains in your PF. Then you need to be able to hold them with patience while the market may give you a wild ride, not exit too early or in panic. So, you need to know enough to build a strong enough conviction in your stock thesis. Then, you need to judge the possible risks, and how bad they can play out to hurt the price from current level or just stagnate for long period. This is probably a part of the first point but must be noted separately also. Finally, you need to see if the factors are attractive enough to be added to your PF and the position sizing (given the others which it is competing with, i.e. the opportunity cost)
Rest all is negotiable, numbers only matter so much, if the price is right given the narrative.