It depends, on what you would like to multiply:
If it's fiat money you're after, then you could stick to trading the BTC for USD's back and forth.
If it's Bitcoins you're after, then you should indeed trade in altcoins.
Regarding a combination of the above two, see for instance this comment of yours:
Wat ik bedoel te zeggen is dat als een Altcoin bv 10% stijgt en ik verkoop het weer dan krijg ik er Bitcoin voor terug. Maar als de Bitcoin op dat moment skyhigh is dan kan het zomaar zijn dat ik dan minder terug krijg dan wat ik heb ingelegd.
In this case, you would have accumulated AND more Bitcoins, AND more fiat money. I'll spell it out for you, in an example:
(not actual prices, but just easy ones for the purpose of a simple example)
- You bought $500 worth of Bitcoin, and you got 1 Bitcoin for that
- With that 1 Bitcoin, you bough a bunch of altcoins.
- Now your altcoins, as per your own example, have risen 10%.
- You exchange your altcoins back into Bitcoin, which would mean you'd have 1.1 Bitcoins.
- Again as per your own example, Bitcoin has gone skyhigh. So let's say that 1 Bitcoin is now worth $700.
- Should you exchange that 1.1 Bitcoin back into fiat, you'd have $770 worth of fiat...