Many people are overwhelmed by the amount of problem sets out there, and so to get you working, I have created multiple checklists for the more important competitions. Here, in order, are the problem sets I will use to prepare.
Math Kangaroo
AMC
Mandelbrot
CMIMC
AIME
ARML
Lehigh
BMT
HMMT November
SUMO
Purple Comet
MPFG
PUMaC
USAMTS
MPFGO
HMMT February
HMMT Invitational
ELMO
IMO
USAJMO
Tournament of Towns
EGMO
USA TSTST
BAMO
APMO
USAMO
USA TST