Took me forever and a day and they still weren't right until I read this:
Buy some Dr Scholls moleskin, it is like sticky-backed felt. Cut a strip about an inch wide and long enough to fit your machine bed from front to back. Put the needle down. Put a Quilter's Quarter or a 1/4" strip of graph paper lined up front to back, against the needle. Peel the paper off the moleskin and lay in in place, being sure that your 1/4" measure stays in place the whole time. (I taped my QQ in place with Scotch tape, I think). Press down on the moleskin to stick. I have had perfect 1/4" seams ever since.....