Most blocks end with 1/2" for seam allowances.
I line my ruler up on the blocks, Look over the whole block and decide where to trim. You don't want to get too close to where there are points, you want to use one of horizontal and vertical lines on the ruler to match to your seams or evenly alongside, to make sure your block will be straight as well as square. You may find you trim more off of one side than the other... but it is best to trim a tiny bit all the way around if you can :D:D:D