The simple rule is "buy at the bottom and sell at the top". But i don't think this applies to all coins, it only applies to solid coins like bitcoin, ethereum and the likes, because they have stood the test of time and would surely find their way back up. But most of these new coins, if you buy at the bottom, the price might still go lower and keep you trapped there. so it is better to wait and see a clear move up before you get on the train to avoid fake outs.
I agree with you that it is easier to invest in cryptocurrencies that are already established in the market, and even if their price goes down, then after one thing it will return to the previous positions and become higher, it's only a matter of time. There are many questions about new cryptocurrencies, especially those whose prices are growing rapidly, and I would not invest in them. But not all new cryptocurrencies are dangerous to invest in them. For example, there are those who have their own working product and their growth is conditioned. I believe that you need to invest consciously and not rush so as not to lose your funds.