Here is a list of hints to try.
1. Go back to the beginning. Are the seams accurate when cutting.
2. If you press, make sure it is an up and down motion so the fabric doesn't stretch.
3. Learn to DRAW a 1//4 inch seam before sewing them. Use a fine pointed mechanical pencil and draw arc lines and straight lines on paper. The lines must be 1/4 inch apart. This is important, as your brain must know a 1/4 inch seam.
4. Figure out where the 1/4 inch mark is on your machine/presser foot. Do this by hand rotating the fly wheel until the needle drops right onto the 1/4 inch mark on a ruler. Use the same ruler to measure, as not all rulers are the same.
5. As you sew, DON'T WATCH THE NEEDLE
5.