A way to remember it:

A lower temperature has a lower number of degrees
A higher temperature has a higher number of degrees.

To decide if -1 is a lower or higher number than 6, you just ask yourself 
the question:

is -1° a lower or higher temperature than 6° ?  Answer: 1 degree below zero is
a lower temperature than 6 degrees above zero.  So -1 is a lower number than 6,
or 

-1 < 6

To decide if -0.02 is a lower or higher number than -0.025, you just ask yourself the question:

is -0.02° a lower or higher temperature than -0.025° ? 

First annex a 0 on the right end of -.02° making it -.020°, so
it will have the same number of digits right of the decimal as 
-.025°.
 
-0.020° is read "negative 20 thousandths"
-0.025° is read "negative 25 thousandths"

25 thousandths of a degree below zero is a lower temperature than
20 thousandths of a degree below zero, so

-0.025 < -0.020

Edwin