Here you don't need to re-watch everything. Just watch these:
Episodes Important to Clark's Storyline:
Season 1
Episode 1 - Pilot (First Episode)
Season 2
Episode 17 - Rosetta (Clark learns about Krypton)
Episode 22 - Calling (Clark starts learning more about himself)
Episode 23 - Exodus (Clark abandons the farm and his "destiny" because trying to live up to it all screws him over)
Season 3
Episode 1 - Exile (Jor-El sends Jonathan to bring Clark home)
Episode 17 - Legacy (Lionel learns about Krypton from Dr. Swann)
Season 4
Episode 1 - Crusade (Clark starts to become more Kryptonian and he starts on a voyage that spans across the entire season)
Episode 22 - Commencement (Clark's season long mission ends when he combines a bunch of relics to create the FORTRESS)
Season 5
Episode 1 - Arrival (Clark trains in the fortress, fights Kryptonians and then loses his powers - he gets them back two episodes later haha)
Episode 12 - Reckoning (Someone close to Clark dies - DO NOT MISS)
Episode 22 - Vessel (The guy who caused the destruction of Krypton comes to Earth)
Season 6
Episode 1 - Zod (Continuation of Vessel, a bunch of alien prisoner's escape Jor-El's prison because of Clark)
Episode 11 - Justice (Justice league is formed)
Episode 16 - Promise (Lana learns about Clark's secret and marries Lex)
Episode 22 - Phantom (Clark fights the last Prisoner and creates a powerful villain)
Season 7
Episode 1 - Bizarro (Continuation of Phantom. Clark's cousin is introduced (blond girl))
Episode 14 - Traveler (Clark's arrival was expecting and there was a group of people tracking him)
Episode 15 - Veritas (Clark learns that Lionel, Dr. Swann, Oliver's parents and the Teagues (from season 3) were all in this cult)
Episode 16 - Descent (Lex kills his father. DO NOT MISS)
Episode 20 - Arctic (Lex discovers the weapon to control Clark but for some reason the fortress collapses on itself (you find out why later))
Intros for Heroes and Characters:
Season 4
Episode 1 - Crusade (I listed it under Important episodes too, but Lois shows up in this one)
Episode 5 - Run (The Flash)
Season 5
Episode 4 - Aqua (Aquaman)
Episode 15 - Cyborg (Cyborg)
Season 6
Episode 4 - Arrow (Green Arrow is introduced - Ollie does come in two episodes before, but he doesn't do much)
Episode 11 - Justice (DO NOT MISS THIS ONE!!!!!!!!! The Justice League forms)
Season 7
Episode 11 - Siren (Black Canary is introduced)
Clark gets new powers (don't really matter, but if you're curious...)
Season 1
Episode 4 - X-Ray (Take a guess...)
Season 2
Episode 2 - Heat (Heat Vision)
Season 3
Episode 10 - Whisper (Super Hearing)
Season 5
Episode 3 - Hidden (Clark jumps RIDICULOUSLY high - Clark also gets his powers back after losing them two episodes before)
Season 6
Episode 2 - Sneeze (Super breath...I'm not joking. Ollie also shows up in this episode)
Season 9
Episode 18 - Upgrade (Freezing breath)
In terms of Season 8 and 9 watch all, but avoid these:
Season 8
Episode 15 - Infamous (**** hits the fan, and then Clark goes back in time to undo everything)
Episode 19 - Stiletto (Lois tries to be a superhero - it's ******ed)
Episode 21 - Injustice (Completely pointless episode)
Season 9
Episode 5 - Roulette (All you need to know is Oliver pulls himself together again)
Episode 8 - Idol (Two "heroes" start doing **** to impress the Blur)
Episode 13 - Warrior (Don't ask...)
Episode 14 - Persuasion (Garbage)
Episode 16 - Escape (Crap)
Also, I took out the episodes with Brainiac. He's pretty much just a computer-person from Krypton which serves Zod and wants to **** up the world. He'll show up now and then.