For a decent introduction (there's a lot of crap on Youtube) this channel gives pretty good info, introductions, and lots of short videos on how to train all sorts of things: https://www.youtube.com/channel/UC-qnqaajTk6bfs3UZuue6IQ
Be warned, once it starts to work both dog and owner can find it (very) addictive. :)
Most impressive thing? First time seeing my dog stop and think, puzzle it out, then try something different. This is not mindless training by repetition.
[1] Edit: Free shaping is leaving everything to the dog to work out with human just providing helpful carefully timed nudges when he edges closer to the right thing. Before long the dog will start experimenting and look to you for reactions a lot more. It's magic, fast, and you'll transform your view of how smart your mutt is.
We had a trainer once who said the hardest thing for a smart dog to do is to just ignore stimuli. You're putting together furniture, cleaning the closet, setting up a stereo, what's that? where does it go? what does it smell like? Is this a game? Can I help?
Smart breeds also need to be kept busy and entertained or they get anxious and angry. They'll start destroying property or fighting with others. If you don't have the time and energy, it's much better to get a less intelligent and mellow dog instead.
The anxiety is enough, it certainly doesn't take (much) brains.
High energy dogs get bored, frustrated, or destructive when not given enough exercise. And a high intelligence just means they're that much more creative in finding ways to amuse themselves (that probably won't amuse you...).
Additionally, part of what makes dogs such amazing companions is their empathy for humans not just intelligence. The current dog of my aunt and uncle is pretty dumb, compared to the previous one. But he loves people, cuddling, and he's super mellow.
He still needs to be walked 3-4 times a day, but not particularly long and he's perfectly happy just chilling and lying next to you all Saturday. That fits much better into less active lives than something high energy that needs to run 10-15 miles a day...
Just pretend you got picked up by aliens who only communicate via flashing lights. After months you might be able to associate certain light combinations and color are associated with food, with being allowed to use the bathroom, with types of interaction, and if you were really smart you might be able to figure out verbs and simple sentence structure, but those lights need to be flashing slowly and distinctly, and if the aliens start using the same light to mean two different things then you're going to get screwed up. For another species to grasp our language is an incredible thing, something no human has ever done, you have to keep things incredibly simple and teach them as if you were teaching language, not just saying what comes into your head.
My dog is frequently confused when he eaves drops on conversations and hears some one talk, for instance, about a long drive to the beach last year, and he waits at the door excited to go. And I have to think why is he waiting at the door, does have to pee? why is he so excited?