A few things ....
Feed dogs might be dirty - have lint in them.
Too much pressure on the presser foot - there is usually a release button on the top of the machine directly above the presser foot.
Bottom of presser foot dirty
Other than the above, a few things that have alleviated that problem for me ...
1) I almost always use a leader to start each piece, and and ender at the end of each piece. I always stop with the needle down and as soon as one piece is finished I lift the presser foot slightly (just enough to slide fabric under it, but not enough to disengage the tensioner) then continue to sew on to the ender.
2) I switched seam guides. I don't use a 1/4" guide that is attached to the presser foot, I use the type of seam guide that screws down to the base of the machine and can slide in or out to the desired position. I then adjust my needle position for a proper 1/4" finished seam. The seam guide I use has a long "rail" that is a good 2" in front of the presser foot which helps me guide the fabric for the whole length of the fabric.
3) Use your left hand to gently guide the fabric through the machine. If the piece is very small and does not present enough to grab/hold with your fingers - insert a long straight pin leaving the tip of the pin at least 1/2" from the 1/4" seam - now you have a "handle".
I quickly set my machine up with my guide and a smaller piece with pins inserted. Photo below. Hope this helps show what I'm talking about.