To keep my 1/4" seams accurate, I use moleskin. This is purchased in the foot section of the drugstore, Target, Walmart, etc. The following method will work only if you can position your needle so that less than 1/4" of the feeddogs are exposed to the right of the needle. (On my Bernina 1230, I have to move the needle one position to the right to achieve this.)
First step is to cut strips of moleskin using a ruler and rotary cutter.
Next, I place my favorite ruler under the raised presser foot of my sewing machine and lower the needle so that it touches the 1/4" mark from the edge of the ruler. Actually, I put the needle a little to the right of the 1/4" mark so the ruler's edge is a scant 1/4" to the right of the needle.
I make sure that the ruler is aligned straight front-to-back, and then lower the presser foot to keep the ruler positioned correctly.
I remove the backing from one of the strips of moleskin and carefully position it so that one side of the moleskin is aligned with the edge of the ruler. I allow the moleskin to extend as far as possible both behind and in front of the needle.
When I sew, I just make sure that the right edges of the fabric are butted up against the moleskin. This allows me to sew accurately even if I am sewing very fast. Before finding this method, I tried a 1/4" presser foot, marking the bed of the machine, using a magnetic guide, etc. but this is by far the method that is the most accurate for me. Some people cut a thick strip out of a roll of painter's tape to achieve the same type of sewing guide, but I have always used the moleskin -- extra-thick if I can find it.
For those who may be wondering, moleskin is an adhesive cushioning material that is used on feet to protect them from shoe blisters.
HTH!