Is this your first placement?
Placements don't matter because you will be put in lower rank because you're still new.
My advice is to master at least two champions in two roles before getting into ranked.
When I did my first placement matches in s5 I won 6 of them and ended up in silver which was hard to climb in because I was getting out-experienced by other players or just straight up stomped by smurfs.
At one point I even got depressed because of how poorly I was doing in ranked that it put my off from it entirely.
My advice to you is do what I did and practice, a lot. Learn several champions, learn tricks with said champions, learn to play around what the enemy does and focus on getting objectives.
This will sound really cliche but practice makes perfect, or in your case it might make you more likely to win ranked games like it did with me.
or you can just get a smurf to help you climb since that's what all the new players are doing.