Getting out of herald

I've played dota since 2020 and don't think I'm particularly bad at it but I've never gotten out of herald. closest i ever got is 600 mmr, I keep rebounding up and down, 10 wins in a row, then tanking back to 10 mmr. as much I would like to blame teammates, ive seen people win games alone to climb out of this hellhole. what heroes could i play to achieve just that, and what practices could I learn to do in games to make sure I can decide them on my own. (i currently play safe or mid lane with clinkz, bloodseeker, lina, weaver, slark, sniper, jugg)