Klavkjir:
Thanks for your reply!
I think that the main problem is that I don't know where to start with choosing a divider.
Could you perhaps elaborate a bit on what's wrong with this value?
I suggest that you look at the page here:
https://learn.sparkfun.com/tutorials/voltage-dividers
It looks like it contains some useful material for you.
In the section headed "Simplifications", there is something relevant to the problem you are having. Read what it says about what happens when one resistor is much larger than the other. (I am assuming that your fuel sensor functions as a resistor whose value varies depending on the amount of fuel.)