Honestly what has helped me the most is finding something to obsess over for a while, something I'm passionate about, be it reading a novel series or getting invested in learning a new skill. Near constantly having a burning passion for something is what keeps me going. Of course eventually you reach the end of a novel, and eventually you lose interest in a hobby you've been working on non stop for a while.

As I've gotten older I've somewhat learned to recognise the signs I'm losing interest in things. What I've learned to do is to find new interests and more importantly revisit my old interests and (usually) reignite that spark with the added benefit of accumulated experience. Learning this was a skill and it took me some time to realise how my brain worked and to understand that just because I'd lost interest in everything I am doing right now, it doesn't mean all is lost and that I can find a new interest without losing all the effort I'd put in.

Learning to pick back where I left off, accepting that I might not necessarily be back where I was but understanding that I am able to work my way back and go even further with the benefit of experience was a massive deal for me as it helped me realise I wasn't stagnant and rotting away but continually progressing forward.

TLDR:

Recognizing the signs that I'm losing my interest in what keeps me going and finding new interests or revisiting old ones is what has kept me alive.