First time owner - what’s the most important DIY skills to learn to keep costs down?

Me (M30) and my Partner (F30) have just purchased our first property - a 150 year old, 4 bed Victorian old dairy.

We are expecting a lot of upkeep and maintenance over the years and see ourselves as custodians of this old property for at least the next 10/15 years and are happy to do as much as possible ourselves.

What are the most important skills you have learnt over the years that have saved you money time and time again?

Any good resources to get started?