Schnurke - It depends on the kind of seam and the material.

For almost all fabrics, the feed dogs should be pulling the material under the presser foot, not your hands.

1 - "easy" material (non-stretch, not heavy) on straight or gently curved seams, with nothing to the right of the needle except the seam allowance.

I was taught that the right hand "steers" the fabric through the feed area by making TINY right-to-left movements, while the left hand moves the bulk at the right to prevent the weight of it from dragging the seams crooked. Just let the fabric run between your thumb and forefinger.

I was also taught to NOT look at the needle - base your guiding on where the material is relative to the seam line markers. I extend the marks (with masking tape) so I have a couple of inches in front of the needle to use for alignment.

When I'm doing these seams, my right hand is usually 6" or more away from the needle and my left hand is to the left of the needle, pushing the fabric as needed to keep it from piling up. On a skinny piece, such as a sash, it's just the right hand guiding while the needle is moving.

The material is held very lightly, so the feed dogs are pulling it through my fingers and I'm sewing as fast as I can and maintain control.

EXCEPTIONS: For extremely curved seams, such as collars and armholes, I have my right hand just in front of the feed dogs and the left hand is right behind them, holding the parts flat, the seam straight and/or rotating it ... very slow stitching, and the feed dogs are still doing all the pulling.

For stretchy material that has a tendency to bunch up the top layer, I use a special presser foot (walking foot) that moves both layers ... if I don't have one of those, I use a 3-finger guiding technique with the top layer between thumb and forefinger and the bottom layer between the next two fingers, with slightly more pressure on the top layer (takes lots of practice, it's easier to buy the special foot.)

Try this: Take some striped fabric and an unthreaded machine and practice guiding the material until you are confident. See how fast you can sew and still sew straight.

TIPS: For a beginner, firm woven fabrics in a medium weight are easiest, as are firm (low-stretch) knits. Avoid slinky knits, super stretch jersey, satins, crepes, fake furs and all that fancy stuff for a while.

Make a few bathrobes, cushions or caftans first. Then learn to handle stretch by making something in fleece or sweatshirt fabric, or modify a t-shirt.

For a cheap way to learn in a fancy fabric, find something in a thrift store that has a similar feel and make a small something out of it. Then make up the pattern in a CHEAP material to get the laterations right ... then and only then, cut your expensive French silk jersey.

When I was a lab tech I used to make my trial patterns in white polyester knit or woven cotton and wear them to work. I was the best dresses one in the lab, because they were Vogue designer patterns.