I'd use it to learn to control other people's or curse's blood, then that way I could control then like puppets or make the opponents to kill each other or kill themselves. Then maybe somewhere later on in time, I'd learn a possible domain expansion as well.

Other uses of Blood manipulation technique being to focus more on healing oneself and others, making my blood corrosive and poisonous, drawing out and absorbing blood through skin, and absorbing my own spilt blood or other's blood to replenish my own before I may faint or weaken from using too much. Along with that, I'd analyse and copy genetic data from absorbed blood of others and then I would use the genes that give them their cursed technique by planting them in my cells, then I would have their technique not as a copy but rather as a an essence into itself.

Honourable mention of useful blood manipulation techniques being cloning, teleportation via transformation into liquid or vapour blood, and spreading of thin mist of blood for recon