As weird as it sounds: try to think like a single dad: as if mom is not the default main character. The reason for this is it is very easy for a dad to defer rights and responsibilities to mom. It is socially acceptable, even. Especially when you're a tired dad with work in the morning.
So doing simple shit like doctor's appointments and taking the kid to a park or grocery shopping without mom's management or involvement can be huge. Be a parent that is a dad. Like learn some developmental milestones that the mother might be tracking and/or worrying about that quite often aren't taught in schools or to boys.
More than just being physically there, being mentally checked in can be huge.
If you are fortunate to have it: take leave from work. I know it isn't an option for many and many employers scrutinize parental leave in general let alone for dads, but my advice is 'Fuck em.' (Maybe take some of that time to find a job that respects a father and family. I did and I do not regret it one bit.)
