The lips are made up of 5 cushions, for the top lip, we have a middle section and two wings that slope downwards. The points where the middle section meets these side sections is where you will commonly find sharper points on the lips. The bottom lip is made up of two round cushions that meet in the middle, for some lips this middle line will appear more prominently.

You will notice that in the example I have left the bottom lip open without drawing in the full lines, simplifying down the details can make it feel more natural than drawing in all the lines. This is a stylistic choice if you shade in your drawings or are painting you would put in the full bottom lip.

Step 1. Draw in the top of the lip using a small curve, I usually start here when drawing portraits because this gives me the placement in relationship to the nose. If you are drawing lips on their own you may want to start with the center-line. Experiment and see what works best for you. 

Step 2. Complete the top of the lip by drawing lines declining from the corners of the center region.

Step 3. Draw the center of the lip, notice how there is a small curve towards the center.

Step 4. Draw an upward curving line for the bottom of the lip.