Imagine a traditional Native American sweat lodge:
In order to heat these up, stones were placed in fire until very hot, then brought into the lodge:
Those would be your positive integers.
Now, let's jazz this imagery up.
Say we could bring in blocks of ice.
Those could be thought of as negative numbers.
So, when you want to raise the temperature of the sweat lodge by one degree, place in a hot stone +(+1)
When you want to lower the temperature, you can either take this stone our -(+1)
Or you can put an ice block in +(-1)
Get the point?
There are lots of variations you could play with in this imagery.
Try it yourself and let me know.