How do we know high-priority Product Backlog Item (PBI) ready? Most of the issue team need to deal in planning is Product backlog item is not enough details so the team is lacking information for forecast what will be developed in the next sprint. 

Therefore the idea for product backlog item is "READY" is created to support Scrum team to pull PBIs to Sprint and turned into product increment quickly. (view image below)
How to define and apply?

So how we define Definition of Ready (DoR) for PBIs? One of technic we can use is  I.N.V.E.S.T for PBIs: https://en.wikipedia.org/wiki/INVEST_(mnemonic)

Independent
Negotiable
Valuable
Estimable
Small
Testable


Conclusion

Same with Definition of Done, Definition of Ready should not be changed but it will be expanded and develop over time as the team will mature every day and know which should do better with PBIs.

DoR also needs to share with Scrum team to make sure it is understood by everyone.