When to dodge?

I was wondering what the opinion of you guys is on dodging. I am low silver and I experience a lot of troll picks, flamers in champ select and people with terrible winrates (for example, somebody with a winrate of 20%, how are you in my game!!). To be honest, it happens like half of the time. When would it be a good call to just dodge and when not to? I feel like I am wasting a lot of lp and time just because I am too 'afraid' to dodge. Would love to hear your opinion in this, ty :)
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