You can be placed as high as goldV on your first ever placement matches if you win all 10 generally 6-7/10 will get you silver 3-2 and 4-5 will be between B2 and SV it depends somewhat on what teams you beat and their ELO (electronic MMR basically for ease of understanding)
Tips;
-
don't rush into ranked play normals
-
find and "main" your best role
-
play normals and get great at 2-3 champs in said role
-
buy all T3 runes
-
have all mysteries correct
-
open.gg for replays to better you play and see what you did wrong (if serious about climbing)
-
objectives over kills
I cannot stress 7 enough if you have all outer turrets and are 9-20 down on kills you'll find your team is keeping up just fine so do not surrender.
Objectives and map pressure win the game not kills, kills help but prioatise the objectives over the kills
edit; if you want to add me I'm more than happy to play normals with you if your Freinds busy and maybe some ranked on my alternate account