For trading shares on CEX.IO -- I mostly focus on GHS/BTC, GHS/USD, BTC/USD, and BTC/LTC trading using an arbitrage algorithm (if I can buy GHS shares in BTC, sell them for USD, then buy back BTC -- that's a solid arbitrage win).
I have scripts that do the work for me. The more capital I have to work with, the larger my wins can be.
There are limits based on the market cap of the pairs I trade. Some don't see the necessary activity to support arbitrage volume, when that happens I'll switch to focus on the highest trading pairs at CEX.IO