If you invest for the medium - long term across a diverse (10-20 alt-coins), you have nothing to worry about. Avoid trading, unless you are really experiences and everything will be fine. I personally keep my portfolio in 20-35% bitcoin which I believe is fairly optimum for the long-term game.
meh, i can't really see this as a good investment strategy. specially these days.
the total loss + profit of 10-20 altcoins is more negative than positive which means you will lose money in total and also it is hard to keep a close eye on 10-20 alts instead of say 5 good rising coins.
and if you look at the market you can clearly see that almost always only a handful of coins are rising (about 5) in other words if you invest in 10-20 you are only getting profit in 5 of them if you are lucky and lose money in 5-15 others.
and the market is big enough for you to invest even all your bitcoin in just 1 altcoin too.