Most successful investment strategy is buy when everyone is selling and sell when everyone is buying which can be long term or short term but definitely it is the most successful one.
A more successful investment will be the purchase of coins at the stage of a private or seed round, when the coin is sold at a big discount. The next stage of the purchase, when you can profitably buy a coin, is the stage of public sale, but this price will be several times higher than the one at which early investors bought.
Isn't it a high risk to invest in a new project? especially when buying private coins or seeds? what if it fails? Are you ready to take risks that you never imagined?
But I believe the OP is referring to the investment of coins that are already in the market so this can choose a good strategy in every trend/hyep, but that also we must be able to get the right one when the trend/hype is no longer popular.
But as long as bullishness is still a positive trend in every strategy, the coins purchased will definitely increase.