Achieve some level of financial security (say 6-12 months savings), then just do whatever you want.
The hard part is the former. Once you've done that the negotiation bit is trivial because you don't really need to care - you can just take it as a given that eventually you'll be paid more (unless you're taken ill and stop/slow down working).
The hard part is the former. Once you've done that the negotiation bit is trivial because you don't really need to care - you can just take it as a given that eventually you'll be paid more (unless you're taken ill and stop/slow down working).