Widespread adoption. This is the most important thing in my opinion. Other things might cause transitory gains or losses but to really move it more people need to use it. It is a scarce resource, and it would need to be divided more driving the price up. Other things obviously factor in but to me this is the biggest.
I think widespread adoption could happen without doing anything for the price. It depends on the type of adoption. Specifically, it depends on how long people hold the BTC and remove it from supply. Let's say you are using BTC to do an international transaction. If you buy the bitcoin in one country and immediately sell it in another country a few minutes later, you'll be "adopting" BTC, but you won't be helping to make BTC scarce. Someone can use those BTC a few seconds later to do the same thing. Maybe you have 100 million people adopting BTC, but they aren't contributing significantly to demand because they are rapidly passing a few thousand BTC back and forth. Adoption as a store of value seems much more important.
