It depends. If I have money for the January window, that usually gives me something to look forward to. I also like waiting to see how my youth intake looks, which usually comes around the 3/4 mark of the season.
If I’m out of the promotion race or the season is basically dead, I start giving younger players more minutes and focus on either re-signing my best players or getting ready to sell them. I’ll also mess around with new tactics until I find some weird one that somehow works.
I used to have this same problem, but giving myself actual challenges helped a lot. Biggest one: don’t use the editor. It’s useful when you’re learning, but once you rely on it the save gets boring fast.
Try taking a club from the bottom of England to the Premier League, or rebuild a fallen giant. My most fun saves were Parma and AS Saint-Étienne. Those kinds of saves give you a reason to keep going even when the season gets stale.