In answer to what numbers we should be aiming for, Tom and Chester from Hotwells Primary School said:

It is better to get the numbers in the middle of the board because then you have more choice and it's easer to get three in a row.

Jeremy from Longston School wrote about what numbers are easiest to get:

I wrote a table of all the pairs the dice can throw, and then the numbers you can add and subtract to get

I then made a table of all the totals you can make, and how many ways of making them there are:

 Result How No. ways -5 (1-6) twice 2 -4 (1-5) twice, (2-6)twice 4 -3 (1-4) twice, (2-5) twice (3-6) twice 6 -2 (1-3) twice, (2-4) twice, (3-5) twice, (4-6) twice 8 -1 (1-2) twice, (2-3) twice, (3-4) twice, (4-5) twice, (5-6) twice 10 0 (1-1), (2-2), (3-3), (4-4), (5-5), (6-6) 6 1 (6-5) twice, (5-4) twice, (4-3) twice, (3-2) twice, (2-1) twice 10 2 (6-4) twice, (5-3) twice, (4-2) twice, (3-1) twice, (1+1) 9 3 (6-3) twice, (5-2) twice, (4-1) twice, (1+2) twice 8 4 (6-2) twice, (5-1) twice, (1+3) twice, (2+2) 7 5 (6-1) twice, (1+4) twice, (2+3) twice 6 6 (1+5) twice, (2+4) twice, (3+3) 5 7 (1+6) twice, (2+5) twice, (3+4) twice 6 8 (2+6) twice, (3+5) twice, (4+4) 5 9 (3+6) twice, (4+5) twice 4 10 (4+6) twice, (5+5) 3 11 (5+6) twice 2 12 (6+6) 1

So it is easiest to make $-1$ and $1$.

It is hardest to make $12$ as there is only one way to make it.