I'd like to ask a question also. Does your machine sit down into a case or cabiner? I find that sewing on a flat surface is very helpful because you don't have to deal with the fabric going up, across the machine, and then back down towards the table top. I think you lose control with that set up. Perhaps, if you don't have a cabinet, stack books around the machine until you have a larger, flat surface to sew on. You can tape the books together, or purchase a clear acrylic table with legs that might fit your machine. I bought an old sewing machine cabinet and my handyman put a bottom it so that it rests flush with the cabinet surface. I remove the machine when I am through and store it in its original case. It really helps when I am trying to quilt on my domestic machine. Also, built a bridge with painter's tape, as others have suggested. I used moleskin cut into 1/4" strips at one time and place it at 1/4" on the face plate, but it is soft and wears down fairly quickly so painter's tape works better. Also, as others have suggested, keep practicing. Do check and see if the feed dogs are working, as others have suggested.

Worrying about your hands may be counterintuitive here. I think it's more important to be conscious of where your eyes are focusing.

Don't watch your hands, or the needle. Focus on the seam line a few inches before the needle. In other words, watch the 1/4" line and try to keep your fabric there. For me, that is the very edge of the feeddogs.

I was teaching my grand daughters how to sew charms together to make a quilt. And I had to explaint his to them to. I had a seam quide thing attached to the base of the machine near the needle. I set the machine to low speed (I know yours doesn't have that...my machine I love is a Singer 2010 from 1985!) but this one is new. I told them to just line up the fabric edge to the seam guide, and for them to just "guide" the fabric through, not push with either hand. The feed dogs will pull it through, so just place your left hand on the side of the fabric, not real close to the needle, and guide the bulk of it AFTER it has been through the needle to keep it straight and the right hand mainly just the thumb and fore finger..they guide it "TO" the needle, keeping it straight. I told them..let the machine do the work! And they did and it worked for them, so I was apparently telling it the right way! I have been seing for 45 years...never thought much about how I did it! KEep at it..good luck..it is also one of those things that just come with practice!

Okay you bright people have mentioned the feed dogs and this is what I was going to suggest as well. If your feed dogs are working it should be relatively simple to feed your fabric into your machine. Hope all these great suggestions help. If your unsure about your feed dogs have your mentor try your machine. She'll be able to tell you if their working properly.

When I was taught to sew, I was told that your hands should rest lightly on either side of your foot..they are to "steer" only, not to push or pull...the feed dogs should walk your fabric through without any guidance from you at all...if they don't, then something is out of adjustment.
This is just for sewing..free motion you do have to push, pull and guide, but that's an entirely different method.

My mother was very stern about my unstraight seams. I didn't sew much because of it. I would sew and see the crooked seams and just put it away. Well now retired and loving to sew, I started taking classes at my LQS. Same problem not one of my many blocks was 12 1/2 inches when finished. One of the instructors finally taught me and many others (seems this is not an uncommon problem) the way her mother taught her. She brought in a cool ruler, it has a hole in it where the scant 1/4 inch would sew. The edge of the ruler would be where you would line up your fabric for that seam. We then took moleskin (Dr. Schules foot products, in pharmacy area) cut it into strips, butted one up to ruler - voila, perfect scant straight 1/4" seams. Luv it and am so proud of my sewing!!!! Wish my mom were alive to show her. You can find one of these rulers at most sewing stores, the moleskin any Wal-Mart, K-Mart, etc. The moleskin is thicker so it is easier to follow than tape. Try it. My last squares were perfectly 12 1/2.

I sew left handed so my right hand is behind thru the throat and to the right of the edge of the fabric behind and my left hand is in front to the left of the fabric and I just guide. I don't pull or push just go with the flow of the machine. I don't know if this will help you at all.

I haven't read all the comments, but when I gave teenagers sewing lessons, I told them it is like driving a car. You simply steer the fabric, not push, pull or stretch. You look ahead of the needle (in front of it), where you are going not where you have been (behind the needle). You don't have to worry about what the needle is doing, kinda like the car tires. If you steer properly, everything will work just great. When you use the "gas" pedal you push slowly, not gunning it. They found these analogies very easy to understand.

My six year old GD made a quilt last summer. She sewed every single square and borders. I only ripped 5 seams out of the whole quilt. I usually rip many more in a whole quilt. The first thing I did was have her guide a piece of notebook paper through the machine sewing on each and every line of the note paper. By the time she finished every line, she could guide the paper through accurately. I have done this with every person I have taught to quilt. I left the thread in because it made it very easy to see how well the lines were being followed. Most adults have it mastered by the time they are half through. It also helped her to learn not to pull the fabric out until the pressure foot was all the way up. It acclimates you to the machine and the fear of the machine usually is gone. I then put the quarter inch foot with the guide on the machine and she just took off. Hope this helps.

Lines on a standard index card are exactly 1/4" apart and are straight. I cut the tiny space on the bottom edge off with paper scissors, turn the card upside down so I do not see the lines, practice sewing. Turn card over and if sewing on the line it was straight and 1/4". Have to cut the card down to the next line to practice again. Cards are so inexpensive. I do this with most every sewing session unless I know I have the machine set correctly for the 1/4".
Practice and watching quilting videos on you tube have helped me so very much.