Large-Scale Scrum(LeSS) is not improved or customized Scrum. LeSS is Scrum. The values, principles and practices associated with the empirical process control which is applied to one team Scrum are used for scaling or should we say de-scaling purposes.
If you know Scrum well, then LeSS would be a cake-walk from "understanding" perspective. However, implementation takes a bit of experience.
One of the fundamental tenets of LeSS is to stop thinking about "Scaling" work rather start focussing on "descaling" the complexity associated with the organization.
Descaling complexity in an organisation involves removal of wastes, identification of bottlenecks, creating a learning culture, reduction of queues and removing the hierarchies associated with Taylorism.
It is not sufficient to know how to do daily Scrum or Sprint retrospectives; it is all about getting deeper insights into Systems Thinking, Queuing theory and Lean Thinking. As one can see in the picture below, the ten principles lay the sound basis to descaling the complexity in the organization.