If you want a fast map of english diction, consume all the standup comedy and prize winning literary fiction you can find. Also, read P.G. Wodehouse, and then watch it performed. Churchills speeches are good to read too. Consider reading or watching Richard Feynman's lectures to get a sense of how a great mind operates.

To be concise and eloquent is also the downstream effect of values that form a personality. It's not something you can affect by imitating, it is the effect of cummulative competence and practice over time. You need the intellectual confidence to ask questions and interrogate your surroundings with benevolent and sincere interest. That confidence comes from finding a kernel of moral clarity that enables you to relate to the world by assuming its approval, to be a protagonist in it, and not a guest or subject who must be meek or deferential to it. Value pith, grit, vision, and humility, but postpone being too humble until you are sure you are great.

"Brevity is the soul of wit," isn't just about humour, it's about intelligence. The essence of english comedy is our surprisingly many synonyms that have wry and ironic collisions in their meanings. Absorbing the comedy practices a sense of humor, which becomes a new sense for interpreting your surroundings. Teasing out the same sense of paradox using humour leads you to the crux of literally every topic. If you can find the joke, you have found the edges of truth and belief.

I used to worry I wasn't being concise until I saw other people try, so take heart.