How to sew straight lines? Practice! And to make it easier, you can use makeshift tools.
1️. Fold a toilet paper tube into a flat surface and cut off a small portion. Stick it (using masking tape) to the working surface of the sewing machine, to the right of the presser foot, placing it at the desired distance. Place the fabric under the presser foot so that the edge aligns with the cardboard, and sew the seam. Thanks to the guide, the fabric won’t shift, and your stitch will be at a consistent distance from the edge. You can move the cardboard guide and adjust the distance as needed.
2️. Use the same cardboard template. Mark lines on the top surface, about 1 cm (3/8”) apart from each other. Fix the cardboard to the right of the needle at the desired distance. While sewing, align the fabric edge with one of the marked lines. Instead of focusing on the needle, keep your eyes on the fabric edge to stitch it evenly along the line.
3️. Fold a piece of thick cardboard in half and apply double-sided tape to the inner part. Attach two old, unwanted needles on top and cover the construction with the other side of the cardboard. Stick this guide to the working surface so that the needles are in front of the presser foot. Place your fabric under the needles, making sure the edge aligns tightly with the cardboard. This method works well for bulky materials (French terry, sweatshirt fleece) because the needles provide additional fabric support.
4️. Attach a magnetic seam guide to the metal plate of the sewing machine at the required distance from the needle (the width of the seam allowance). Thanks to the magnetic guide, there is no need to closely monitor the presser foot or mark the exact width of the seam allowance while following the needle. The fabric edge tightly aligns with the guide during the sewing process, resulting in straight stitches.
5️. Use an elastic hairband. Put the hairband on the free arm of your sewing machine, positioning it at the desired distance from the needle, and sew your stitch along the fabric, using the hairband as a guide.
More sewing tips for beginners are here: