It's require consistency and you have to target the areas which are important for your work also differ from field to field some are changing rapidly like computer sciences or Medical sciences.
my field is education and i know little about it, What would be the best starting point for me? How do I find and focus on the content I want? When I have no deep knowledge of this field...
1. Threshold Concepts. (See https://www.ee.ucl.ac.uk/~mflanaga/thresholds.html) . A threshold concept is a 'big idea' - you can't half understand it; it's 'all or nothing'. - I would say that mastery in a field means that you have mastered the threshold concepts, and everything else follows from that.
2. If you want to understand education, I'd say have a good look at the process of habit formation (Duhigg's book is an easy read). I've been at teacher for 8 years -- We don't look deep enough at habit formation, but I think this is crucial for creating deep change. You could also look at the idea of 'Teaching for Transfer' - Transfer is the ability to generalise a skill/knowledge from the context in which it is learned to another context. If your students are 'transferring' knowledge and skills, they've 'learned.'
I would consider it risky to say you have to learn all techinques. What if there are many techniques? Plus, what does 'to master a field' precicely mean?
Certainly the more you know there better you master it. But in reality, this is complicated.
Learning never ends! You cannot learn everything! However, you can master what you have learnt through practice, build on it, and learn new core techniques that are important and useful.
Natural and applied sciences are expanding and deepening every day. And specialization in the field of precision in a branch of science is predominant today, so to be good researchers we must focus on a precise branch of science in order to be creative. This means that we cannot know all the details of the scientific branch in which we work.