My daddy always said I was born with a crooked eye, and my son agrees because I cannot hang a picture straight. There are a couple different ways to get your 1/4 inch seam. You can buy a special 1/4 seam foot with a guide to help you when you sew your fabrics (this is what I have). You can get a ruler and measure a 1/4 inch seam from you needle and place a piece of tape on your plate of your sewing machine so you can align you fabric.
As far as cutting practice and go slow. Walk you hand up the ruler carefully to give you more control when you cut your strips. If you move the ruler, you can sliver trim and try again.