Do not let the name fool you. The "flat iron" can be used to create many styles other than just a bone straight sleek look. You can create styles with volume, texture, flips and curls as long as you know which way to turn the iron as you are styling your hair and what products to use.
Creating ringlet curls in your hair can be best done with a smaller iron. The plates should be 1/3 "wide or smaller. You can create ringlets with larger plates; however the resulting style will be more like waves than ringlets.
Also make sure that you are using a quality flat ironing tool with ceramic plates. At least make sure that the plates are ceramic coated, if you do not want to spend a lot of money. The worst and most damaging kinds of irons are those with straight aluminum plates. Avoid aluminum at all costs if you do not want to damage your hair!
Always start a new flat ironed style with clean and conditioned hair. When you flat iron dirty hair, you infuse your hair with the dirt, burning the dirt into your hair follicle and into the flat iron plates. It can be damaging to both the hair and the iron.
Next apply a smoothing serum to your hair and blow dry or allow it to air dry. Depending upon your hair texture, it is usually best to blow dry if you want to create the best looking final style.
After your hair is dry plan out your hair style by putting in a part where you want it, or at least decide how you want your hair to fall. This is important as you are styling so that you know which way to turn the curls.
Creating the curls from this point is easy. You start with the flat iron positioned close to your scalp and you slowly rotate the iron into a curl. Bring the plates down the length of your hair while still curling your hair into the flat iron. The best way to truly learn this is to search for a video to watch on YouTube.
For the best looking curls, you should change directions with each section that you curl. This creates a natural looking curl pattern. Think about it: if you had naturally curly hair, would all of the curls go perfectly in the same direction? No way. So make sure that you alternate going in the forward direction toward your face then backwards toward the back of your head as you curl.
Finish the style with shine serum and hair spray or finishing polish as needed.