It sounds to me that you need to look at your presser foot settings which is so important but difficult to get right until you get the hang of it. Here is a Youtube video that may help you
http://www.youtube.com/watch?v=Ox8qRhWF3CI also an article
http://www.westsidesewing.com/wss/tips/art_pt08.pdf
The other tip I would give you is that a lot of quilters recommend a walking foot for quilting, which works but are quite expensive I don't use one for other reasons, I don't like the noise and not being able to see where I am going clearly so I use the tip by Nancy Johnson-Srebro and use a wide toed see thro' plastic SATIN foot, works like a dream and is normally supplied with your machine, if not they are cheap enought to buy.
BTW I normally do my first stitch line straight down the middle, top to bottom, of the quilt, check there are not wrinkles etc; and then turn the quilt around and do a line side to side. Then quilt a quarter at a time.