I generally upgrade what money making facilities that I can (sausage stand restaurant etc),upgrade my stadium by 500 at a time if its selling out,do the math on whether its worth upgrading parking/toilets. It's personal choice if you want to upgrade youth and training,I personally go slow on it to begin with.
I then look for a scout (and formerly coach) to hire that is an improvement on a current one,or just a new one if I feel the need to add 1 to my staff.
Then once facilities and scouts are done, I use what's left over to upgrade players in my team. Whether its a better player in a position,or a similarly skilled local player to replace a foreign one,or even a similarly skilled (or better) younger player to replace one that is over 33-34
Different people have different strategies though. That's just part of mine.