I have a lot of trouble against zed and fizz.

I really don't know how to play against them. I understand flask or cloth Armour start is your best friends and counterpicking and blah blah blah get a seekers but sometimes you can't counterpick and a flask can only take you so far. Are there any tips against them? Sometimes I feel like the only option is to just sit under tower but is there really anything else? This is more about zed and yes I did get rekted by one but I do really want to improve. Any tips ?