Tools, Tips, Technique
Tools: There are 10 or so different 'professional' curling iron sizes. For the public, 3-4 sizes are readily available. The heat will vary depending on the product. Professional irons are extremely hot compared to those that cater to the non-professional.
Place a 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 before you start styling will remove the moisture from it, even if it does not seem damp sometimes the scalp has moisture or the air is humid.
If the irons are difficult to clean I find nail polish works well to remove residue. Of course always unplug your tools to clean them.