Darren Hill gets credit for this idea, but I'm modifying it a bit.

It can be tricky to determine how long a certain Advantage should last, how it is "cancelled" and such. So, instead of dealing with all that, here's a simple way to handle how long Advantage dice stick around.

Every time you add an Advantage die to a roll, it is reduced in size by one. This happens after the roll. When the die is reduced below d4, the Advantage is lost.

Example: I get a 1d10 Advantage die. Later, I add it to one of my rolls. After the roll, it becomes a d8. I can use it 3 more times (d8, d6, d4) and then it's gone.

When using the above rule, I also modify the Advantage dice table to this:

 Victories     Advantage Dice
    1              1d10
    2              2d10
    3              3d10

And so on.