Placements jg role

I'm a jg main and just did my placement been playing for the last 2 years ( on smurf acc ) I been stuck in low elo for 2 years and I'm so bad like I'm awful my decision making is horrible everything else is decent . I just did my first placement match in high silver and low gold elo and I went 2/6 now please give tips on how I can go 6/2 I want to get good at league ive heard all the tips but I want to get high gold. Is there any high elo players that can tip me ? Also how come a high elo jg can go 20/0 in gold but when I try I suck what do they do that I don't , ty.