What is the best technique to conceive a boy?

You get what you get. Unless you have lots of cash and involve a fertility center to select a boy embryo for IVF, there is no "method" to get a boy. Timing/diets/positions/etc are all myths that linger because they work half the time.
IUI. I believe that selecting sperm via a technology that seperated male and female sperm is available. Otherwise I am not sure of a reliable method but look up sperm and vaginal ph. There may be a correlation to the vaginal environment and the survival of male vs female sperm. I think the relationship is marginal but look up the topic.