Does your machine have a threading diagram inside the front drop down cover over the loopers? Many machines have a diagram here which includes red dots for oiling points.
Usually a couple of spots where the loopers move through/over another metal part.
Important to firstly brush out the whole area underneath the needle plate, around the blade, and the loopers and inside the case area completely, removing the lint with a brush and cleaning it into your bin. The lint waste will absorb any oil so clean it out with each use.
Then apply the oil to the looper points.
You should also rub a little bit onto the blades, you usually can lift the upper blade/swing it away from the lower so do this and clean them both with a cloth that has a dab of oil on it, then lower it back into position.
Then serge for a bit on waste just to make sure its not too oily on the blade for your good fabric.
Hope this assists you, I'm guessing you don't have the manual but always good to obtain if you can - you can buy one here.
http://www.sewingpartsonline.com/instruction-manual-brother-925D.aspx