New pc

If you're using a HDD as opposed to SSD currently, I recommend picking that up first and seeing if the performance improvement is sufficient enough to hold off a while on a full upgrade (and save a little extra cash for it in the meantime).

Typically I do incremental upgrades (e.g. adding RAM, drives, PCI cards, etc.) until it comes time to upgrade the CPU at which point I do a full upgrade and replace the motherboard, PSU, RAM, CPU, etc... sometimes I'll swap the video card over depending on how old it is.