I just realized this was about joining league's, I'm probably going to leave my rant here in case anyone's curious though

If you have time

A lot of being good in Crucible is skill based, but a lot of it is also about your loadout. Do the weekly heroic strike at least once a week in case a high tier pvp exotic shows up at Xur's (Red Death, The Last Word, Mask of the Third Man, etc).

Things to think about before a fight take the time to note who's playing with and against you. While you're flying into orbit if you go left from the start screen you can inspect other players and find out what setups are being run by people on your team and on the opponent's team.

If someone is a level 32 with the Thorn and a sniper you can easily shotgun rush them. If everyone has Gjallarhorn's on the other team you probably should hide out until the first volley of heavy ammo is spent. If a teammate or two have Praedyth's Revenge/Mida you can rush knowing that most kills you fuck up will usually turn into assists.

Things to think about during a fight

Be willing to adapt midfight. If you're continuously losing shotgun duals to another player, either due to lag or skill difference or just plain bad luck, switch your loadout and try different engagement lengths. If someone kills you holding a shotgun with their shotgun 5 times, they're not going to expect you to have an assault rifle waiting the sixth time.

Things to think about after a fight

Keep an eye on how your fights went and what gun beat what at what range. For instance, for the next fight if I'm going to use the Invective to get around the special ammo nerf, I NEED to know that it is outranged by the Felwinter's Lie and the Secret Handshake, so I need to get in even closer where I can afford to miss a shot (auto fire mode) and they can't. If I'm going to use Secret Handshake, it helps to know that I'm not going to get another shot if I miss, so it's okay to take advantage of my range and take an extra millisecond to track my target.