I am quite a practical thinker so probably use some techniques that you might not find in a magazine. Here I was teaching a photographer how to control the output power of his DSLR pop-up flash. If the flash is too bright and he is using ISO 100 and at f2.8 to obtain a shallow depth of field and he doesn't have an ND filter then what next, if keeping the same composing using a prime lens without PP cropping? If you want the flash to be 1/3 power output then cover 2/3 of the pop up flash with you finger, half power, cover half of the flash and so on. It sounds simple but it works. I rarely use pop-up flash as for starters Leica M cameras do not have a pop up flash but if I was in the same situation with say a Nikon then this is how I do it.
Candid photo taken with a Leica M9 of model Gina posing for the 1-2-1 Coventry photography workshop
More info here - BLOG (New) :
mrleica.com/2014/09/09/non-leica-dslr-pop-up-flash/ 