This is a very basic way of generating LP, with the dagger in hand you can right-click to start stabbing yourself, this will slowly fill the Altar up, each stab will get you an un-upgraded base of 200 LP (200mB of liquid ) at the cost of 1 full heart (2 health). This is not very much but if you have food or healing potions handy it could be very beneficial.
Warning: Stabbing yourself by spam clicking the dagger CAN and WILL kill you, some packs have a gravestone mod installed and there is a known bug that if you do kill yourself there maybe no gravestone. Please do this with an empty inventory or be very careful.
There are a few other ways to generate LP: