Tokens must be held for a decent period of time just to approach to pre-sale or ICO price.
Most of them will never do it so it's up for you to decide.
Where to sell? Open CMC and see the exchanges tab.
For how to know which tokens are not on the exchange how? and how to sell the token how? honestly I have never sold my token once
But also there are a lot of fresh tokens that have small volume, you can monitor ANN threads to find out where are they currently trading.
To sell tokens - in a centralized exchange - create account and then send tokens to an exchange's token wallet. Than place your orders sir