Do the opposite when the negative sign is acting as a subtraction symbol. For instance, if your problem is x-3=5, you cancel out the negative 3 by adding 3 to both sides. So the problem becomes x=2.
Add a one in front of and x with a negative sign. So, -x=5 can actually be written -1x=5 because you actually have one x.
Multiply or divide a negative by a negative to get a positive. So if your problem is -4x-8=-12, you divide the entire problem by -4 and are left with x+2=3.