I am on verge of getting demoted

Guys I just reached siliver after years of hard work😊 but I am now -3 lp Bec I left champ select and lost the other game and since I haven't won any ranked matches after reaching siliver I think imma gonna get demoted soon and I don't want that to happen so any help would be helpful on how to be better should I play top or jgl or bot which one is great at helping your team win thx.😀 And I also want to know how much do you lose at 0 lp in order to get demoted