Two pieces of advice to start with :
Never buy the most expensive cards (like 1080's or the new volta pascals etc) buy the ones that offer good performance/$ like the GTX 1060 or the RX570, that gets you to ROI faster.
Never mine multiple coins, mine ONLY whatever is the most profitable AT THAT TIME and exchange it for other coins if you think they will go up more in the future.
Thanks for the advice.
That is a good advice, but stay away from cloud mining, thats really stupid.
Before you proceed, you really need to research hard.
Best ROI is on GTX 1060/6GB or RX570/4GB, RX580/4GB.
Rigs with 6 cards, or even 8 with 2 PSUs.
Cheers mate.