Is there any way to plan the sex of your next child?

No. There are a number of old wives tails and con men pushing a certain products, but there has been no good scientific studies that showed anything works better than just random chance.
DEPENDS $$$$$. If you are ready to undergo egg harvesting,petri dish fertilization and implantation of a gender specific embryo by a fertility center, you can select fetal gender, if it works.Otherwise, the myths about timing/sexual position /etc are just that, a myth.You get what the sperm that arrives first produces.