Just imagine what is annoying for other high-roller crafters to craft. Craft those items that crafters need in order to synth the final product. You can make gil on high end stuff, but you can also make gil selling intermediate/supplemental materials. Look through your recipe book, check the markets, and determine what investment and profit-margins that you are comfortable with. Some markets have lots of competition and undercutting but you can find other areas with less competition.
Neglected markets like old Relic items such as Kingcake, Titanium Alloy Mirror, Adamantite Francesca, and Dispelling Arrows can still be quite profitable as well.
Raid food like Steamed Staff are pretty popular and sell for a decent profit, especially since you can make 3 items per synth now.
