It depends on how many episodes you want to watch from those seasons. I am not keen on most of season 1 episodes with a few exceptions, but some of them are important for the development of characters. "Past Prologue", the episode that immediately follows "The Emissary", immediately starts the development of Kira's character by introducing a character from her past as a terrorist/resistance fighter and forcing her to make decisions about where her loyalties lie; also, Garak is introduced (extremely interesting character, who is many people's favourite DS9 character). "A Man Alone" and "Vortex" introduce a lot you need to know about Odo and his unique position as a Changeling who has never met any other member of his race. "Captive Pursuit" is a standalone but an excellent one.
The best episodes, that absolutely
should not be missed, are "Duet" - one of the best episodes of DS9 and the one that made me fall in love with the show, a really strong and moving story with several twists, with a great performance by guest star Harris Yulin as a Cardassian who might or might not be an infamous genocidal war criminal; and the season1 finale, "In The Hands Of the Prophets", which introduces Louise Fletcher as Bajoran religious leader Winn, who is one of the show's great villains.
I actually liked at least half of season 2 episodes, so I'd almost find it easier to list which one you should skip.
The ones I think you need to see, either for the important plot points or because they are simply very good:
The Circle trilogy - "The Homecoming", "The Circle", "The Siege" - show's first three-parter, shows the series dealing with more seralized plots involving Bajoran politics; Winn continues to play a big role.
"Cardassians" - very good episode, and it develops Cardassians further (well, obviously

)
"Necessary Evil" - excellent Odo/Kira episode about Kira's dark past during the Occupation
"Whispers" - an unusual and excellent O'Brien-centric standalone episode, a bit like a psychological thriller with a real twist.
"Profit and Loss" - I'm not completely sold on Quark's story in this episode, but it brings even more complexity to Cardassian society, and has some great Garak moments
"The Maquis I/II" - good two-parter, and Maquis and Sisko's attitude to them will constitute an important storyarc in later seasons; also, this is where Dukat gets more interesting and ambiguous as a character, rather than just being the constant antagonist
"The Wire" - great episode about Garak and his mysterious past that keeps you guessing
"Crossover" - the first (and best) of the DS9 Mirror universe episodes
"The Collaborator" - an important development related to Bajor and Winn
"The Tribunal" - I just really liked this one. It really shows the scary side of the Cardassian authoritatian state and judicial system.
also, you may love or hate "Blood Oath" - it all depends on whether you like the Klingons; if you do, you'll probably love this episode, which brings back the (retconned versions of) the three most prominent Klingon characters/actors from TOS (Kor, Koloth and Kang). I don't really like it much, but I don't really like Klingons much in general.
