Since the first term in the equation is 
, you know that each group you make will have to have an x in it. Now, you need to figure out what times what equals 7 and adds up to 8. You can list all of the numbers that multiply to seven until you find the right numbers.
-1 x -7
1 x 7
1 and 7 add to eight and multiply to seven, so those will be the numbers in your groups. This makes your factored groups (x + 1)(x + 7).
-1 x -7
1 x 7
1 and 7 add to eight and multiply to seven, so those will be the numbers in your groups. This makes your factored groups (x + 1)(x + 7).