I bought some BTC/USD and ETH/USD when this week's bear market started, and am down a fair amount from then. I should've waited longer, as least before doing buys of the size I did. I think Luc's advice above is very good - let it go down a fair amount before buying in. We could see this bear market / correction continue - god knows everything's gone up like crazy the last 3 months.

EDIT Sunday morning: Holy shit. What a breathtaking drop. Nice to see something I said turn out to be wise!