Tools, Tips, Technique
Tools: There are around 10 sizes of 'professional' curling iron. For the public 3-4 sizes are readily available. The heat generated by the iron will vary depending on the product. Professional irons are extremely hot compared to the ones available for amateur use.
Place the section of hair between the gutter and barrel and roll from root to tip to warm the hair first before curling. If your iron does not have a gutter simply preheat the hair before curling. Warming the hair will prepare it for styling by removing the moisture from it, even if it does not seem damp sometimes the air is humid or the scalp has an excess of moisture.
If the irons are difficult to clean I find nail polish works well to remove residue. Of course always unplug your tools before you clean them.