I think writing down your objectives and results you'd like to achieve are good. Writing them down is itself a form of positive thinking and self-help; they're "just" words, and there's no limit to what you can write.
And then review your progress at some velocity that makes sense (weekly for some, monthly for others, quarterly or thereabouts for the rest) to see if you're on track, if your objectives have changed, etc.
But the book Switch by Chip and Dan Heath kind of opened my eyes to the danger of "SMART goals" / self-motivation. They talk about the "rider" (your rational, critical inner voice) and the "elephant" (your emotional id-like creature) and how you have to get both working, and OKRs and the like satisfy the rider but don't reach the elephant.
They recommend for example drawing up a "concept poster" or postcard (similar to Amazon's "future newsletter" touting the success of a proposed initiative) to really get alignment on what will get you excited to do the good things you want - health, wealth, family, community, planet, whatever - without having to prescribe it to a chart or metric.