OC depends very on your specific card.

For ETH i would put Core Clock down by 200 or 250, Memory Clock up in 50 Steps starting with +200 (with my card i can go easy do +500).
TDP i would limit that Voltage is ~ 0.950 - that keeps also temperature of the card lower.
For ZEC and other similar currencies go with Core Clock in 25 Steps up (mine runs at +100) and for Memory Clock the same. TDP again that voltage runs ~ 0.950.

I get on ETH 29.5 MH/s with 55% TDP, -250 Core Clock and +500 Memory Clock (but the MSI GTX 1070 Gaming X 8g has high TDP  and high basic values for Core and Memory already)
For ZEC i get 470 MH/s with 65% TDP, +100 Core Clock and +500 Memory Clock.