Welcome to Bitcoin/Cryptocurrency world buddy. If you do really like to make some trades between these coins then as a begginer or complete newbie you should know first important fundamentals to consider first before tending to jump in into trading because its not really easy on making money, you should really be knowledgeable to make profitable trades.Talking on when to invest on btc and eth is when the price is on its dip or lowest because once price do goes up you can make profits on it when you decide to sell.