I use the mylar strip for contact and bulk only and don't really focus on anatomy.
This is what I do for maxillary anterior teeth, specifically #8 and 9. First, I put a wedge in. Then the mylar strip goes around making contact with the adjacent tooth. At the same time, I'm making sure there's a little bulk at the buccal by adjusting my thumb to move the mylar strip mesially or distally and I'm also lightly pressing with my index finger to form the lingual fossa. My thumb is resting on the adjacent tooth and is not touching the prepped area. So what does this look like? My thumb is at the buccal, resting on an adjacent tooth, and my index finger is at lingual, resting on the prepped tooth and lightly pressing the prepped area where the lingual fossa will be. They're both holding the mylar strip but are serving different functions that I just mentioned.
Here's the important stuff concerning anatomy. You're going to leave the wedge in place and then remove the bulk at the buccal with soft lex disks from all angles. Move from 9 o'clock, 12 o'clock, to 3 o'clock while moving the patient's head to better see the line angles and contour from all angles. If you were right handed, were at the 3 o'clock, and were working on #8, you would move the patient's head to their right and use the disk to contour the facial, distal, and mesial contours. Repeat for all positions. As you go around, you may have to remove the disk and flip it over in order to orient the hand piece the way you want it to. A good finished product would reflect light at the line angles, which is what your professors are looking for. This reflection of light at a correctly positioned line angle is what you're aiming for with the soft lex disks.
For the lingual, I would use a football bur to make the fossa and ridge. The interincisal embrasures can be made with careful use of the soft lex disks and football. The interproximal contour is made with the thickest wedge in placed as possible and with a soft lex disk. Get rid of interproximal flash and bulk by carefully using a finishing strip. Be careful to wrap the finishing strip around the tooth so you don't make a flat ditch. I also use a skinny football to make the interproximal embrasure as I move gingivally.
If your school makes you get rid of the cavosurface line angle at the buccal aspect in order to make a transitioning appearance between tooth structure and restoration, I would use a fine grit finishing cup to smooth over the area where composite meets tooth. I would also press relatively hard, close to the point of burning the cup, in order to remove buccal bulk and flash, if there are any, with the finishing cup. Use water to prevent burning. The finishing cup wasn't designed to remove fake tooth structure but it does a really good job at doing it while smoothing your restoration if you press hard enough. You could also use the flat finishing disk on the interincisal embrasure and interproximal.
If you really, really, really suck at using mylar strips, try adding excessive bulk by having the strip make contact with the adjacent tooth and then even more by slightly overlapping over the contacting tooth. It's sort of like when you press your finger against an inflated balloon, the balloon would envelop around your finger. Do this if you have trouble making decent anatomy because it's easier to remove bulk to form anatomy than to continually add composite to form that anatomy.
