I noticed that I can't get into the drama just based on the first episode. I rarely enjoy the first or even the second episode, so I try to never drop a drama just after watching the first episode. I noticed that some people do that, though. Can you really figure out if the drama will be good based on "first impression"? Thoughts?

I do my research before starting a drama, so if I start the drama there's a 96% chance I'll finish it ... even if it gets bad toward the end. However, it's not unheard of that I drop shows, but it takes a lot for me to drop. I can complete a show that I truly hate, like say, Temptation or The Heirs, but will drop in a hot minute shows that are too idiotic & childish, i.e Fated To Love You (k-version). My point is even on those rare occasions I do drop a show, they're dropped after several episodes, never only one. I don't think I can really know if the drama isn't for me after just 1 epi.
I think there are several I've dropped after one episode, but they all tend to be those dramas I try out on a whim.  Anything I've actually been anticipating or paying attention to to any extent at all I'd give at least an episode or two more before giving up.  But sometimes I just start things randomly that I never expected to watch at all, so I don't feel bad dropping it (and not giving it a chance) if I didn't intend to watch it to begin with ;)
Occasionally I will if I really dislike it but I usually like to give it a bit more of a chance before dropping it. Some dramas just have a slow start.
I am guilty of that, on few occasions I did drop at first episodes, may I hated the main couple, may be I disliked the way the episode is film I don't know. Usually I wait until the 5th episode before it is officially out though
I've done this multiple times and still haven't learnt my lesson lol. I'm very ehh about many dramas and have even dropped dramas like W - Two Worlds and Healer... Only to come back to them and completely regret my decision of dropping them. 

There have been a few where I have completely dropped (Usually Romances and Comedies or the "School" theme). It just really depends. Usually I can sit through the first episode but then drop them at the second.
I try to avoid that at all cost unless something really gets on my nerves in he first episode and I struggle too much to get through it, but I try to never drop a drama just because the first episode is weird or the story is slow. Now  that I think of it, I do sometimes decide that the characters drive me nuts and I just can't continue no matter what ;)
Pinocchio was hard to pick up... I tried to get past the first episode like three times because there was a flashback that lasted for almost the entire first episode, but after the second episode it picked up and I am so glad i finished it xD You should probably watch until the fourth episode to judge it. 
Sometimes, if I really can't stand it. Then sometime later, I try to watch it again.

I usually give a 3-episode rule lol
I'm usually pretty selective about what dramas I start, so I don't drop many shows.  Occasionally I will start to watch something on a whim, but if I really don't like it, I'll know right away, usually in the first 15 minutes.
Even if I hate a drama by the first episode, I will usually not drop it unless I get past at least quarter of the show and I still hate it. I used to not drop dramas at all, but ever since I forced myself to watch BOF completely, from start to finish, I realized that it's better to watch something you like then waste time on hoping a terrible drama will get better as you keep watching.
i too rarely drop on first ep unless it smacks me in that face that it is just bad or it makes me mad for some reason.  
I generally stick to the 4-episode rule before deciding to drop or not. Before I watch any drama, I do research. Tons of research (rip). I look into the writer-nim and PD-nim, cast, plot, etc etc. Some dramas start off okay, but then go downhill. A few other dramas start of slowly, then pick up. For example, I was okay with the first four eps of Bride of the Water God, but it got reallllly boring after that, so I dropped it (I tried to stay for NJH but couldn't). I had to try Reply 1988 three times before getting into it (currently #2 in my top 10). I rarely drop after the first episode, but when I do, it's on the dramas that feel messy from the start or because the characters are terrible. hope this helps :-)
It may happen, but usually I give drama '2-to-4-episodes chance', sometimes even 6 if I am here-and-there with the drama.

I usually try to stick to the 4 episode rule, but sometimes something annoys me so much I drop the drama after the first episode.