1. Get a 1/4" foot for your machine. This foot has an extra piece added along the edge of the foot. When you’re sewing, you simply run the edge of your fabric along that guide sort of like a bumper. This helps you sew a straight 1/4” seam every time. If your machine doesn't have a 1/4" foot, you can make your own guide. See our instructions here.
2. Sometimes when you start sewing two pieces of fabric together, the pieces can get pushed under the needle at an angle. Try using a little fabric scrap underneath your machine foot when you start. Start sewing right off of that scrap, so you can go straight onto the pieces you’re sewing. It's the perfect way to make sure from the very first stitch that your seam is straight.
3. Slow down. If your machine has an adjustable speed control, move it down to one of the mid-range or slower speeds. It'll give you more control, which can be very helpful in keeping your seams straight.
4. Always use your needle-down option if your machine has that. When you’re sewing and you stop to remove a pin or readjust your pieces, your fabric can slide. If that happens, when you start sewing again, your seam won’t line up. Always stopping with your needle down in the fabric will prevent this. Then when you start sewing again, you’ll start right from where you left off.