To be adept

The most valuable skill you could ever develop is the skill of directing your thoughts towards what you want - to be adept at quickly evaluating all situations and then quickly coming to the conclusion of what you most want and then giving you undivided attention to that.

I saw the above on Facebook. I am learning to write longer sentences using various methods and structures discussed in various online materials.

The most valuable skill you could ever develop: the subject of the sentence

Is: main copular verb

the skill of directing your thoughts

towards what you want-subject complement, an independent clause

Is "To be adept..." an independent clause or a subordinate clause?

what is its grammatically function in the sentence-adjective or adverb?

Has "to be" got any specific function in the given context, apart from marking the beginning of an infinitive phrase?