How to improve "Solidity"

I mean I guess playing d4 and trying to get positional games or going for simplifications and endgames would be some of the "obvious" answers... But I thought some stronger players might have some more nuanced answers on this so I thought it's worth a discussion...

Cuz tactics improve your calculation, visualization, patterns, but ultimately what you are actively doing is looking for the -best- move, not "a solid move"...

Books may improve strategy and positional play...

But my question is slightly different... how do I train at becoming more "solid", or like "eliminating mistakes" from your game.. working on improving consistency and to regularly be more stable, calm, and in control?

It also relates to defensive skills I guess..

Please share your tips

Thanks!

Focus on prophylaxis.