Just trust your instinct and have a lot of patience. If you really want to do it effectively, research some potential coins that you really want. By the time you bought a certain coin do not bother about the market, just ignore the downs it really happens and just set the amount you want when you think you earn a good profit.
If you invest in any coin after a extensive experimentation and have choosed a top coin then don't worry about the price Fluctuations because top coins does not goes down forever and they never loss their complete value. In case of altcoins which are newly emerged you should be worried about dip as they are strenuous to trust.
You can earn during Fluctuations only when you have forbearance but if you become afraid of lossing when the market get dumps then i don't think that you will continue your investment till the winning of your target. Solana is more preferable coin these days and if someone don't have invest in it then he is not serious about taking profit because only this coin show more worthiness among altcoins.