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Set a simple goal, like: whenever I earn 20%, I will exit

You can set goals for yourself but FOMO (fear of missing out) is always around the corner. Try to investigate what a coin can be worth. Not in terms of value per coin but the marketcap. For example I give you Steem. It contains services like Youtube, Facebook-like, Reddit, Soundcloud and many more. If you add all marketvalues of that companies together you will easily reach 100B plus. Steemit is not even 1B at the moment so it is very lickely that Steem will raise substantially.

If you are a technical trader try using 3 indicators which you master. If 2 out of 3 indicators tell you that the market will reverse, buy-in or exit!