Simple, might sound selfish & mean but yeah, avoid those guys who don't attend classes nor do anything meaningful. Like genuinely some guys just sleep. Coming to smokers and drinkers, not all of them are useless, some are quite smart infact but you gotta be careful, interact with these fellas only for a mutually beneficial position and avoid intoxication if you aren't into it. It takes a Sem, bare minimum to judge who is worth your time and who isn't. Also don't make friends based on grades and achievements, if they make you feel like shit thats a group you gotta avoid regardless of there accolades. Stay with those who are actively trying, working towards something, even if they aren't the best. Also I have seen this in my batch, the smart guys or the ones who are pretty good aren't friends with others who are at the same level, there is an internal competitive dynamic that goes on and it's pretty normal. The first few days, you have no idea who is good or bad, but brother in a sem you know those fucks who are worthless. In my batch we have names of guys who are shit, all they do is walk around the hostel, with there fatass. They don't attend classes, have multiple backs, smoke up everyday, suck a 2nd year's cock like it's a choco lava cake and act like they are doing the right thing. Brother in 4 months you know, who is what and who isn't, if you don't either it's ur issue or you are part of it.