plot the given points and draw the side of the parallelogram

Draw in the two half-diagonals:

To go from (0,6) to (-1,3), you have to go 
1 unit left and 3 units down. So to get the
complete diagonal, start at (-1,3) and do the
same thing. That is go 1 unit left and 3 
units down, like below and you end up at (-2,0):

Similarly to go from (3,1) to (-1,3), you have to go 
4 units left and 2 units up. So to get the
complete diagonal, start at (-1,3) and do the
same thing. That is go 4 units left and 2 
units up, like below and you end up at (-5,5):

Now you can draw in the complete parallelogram:

Edwin