the most important lesson I've learnt is to never trust those who tell me which altcoin is "hot" right now and also to never bag hold any altcoin for more than their pump can last. for most coins that I trade it is as short as a day since that is how long pumpers are going to pump that coin but it can go as big as a week mainly for bigger coins that don't get dumped that easily but get dumped all the same.
this shaped up my overall strategy. I accumulate bitcoin (long term investment) while short term trade altcoins to increase the number of bitcoins I own.