actually arbitration will be more effective if done when there is a striking price difference so that we will receive profit and not lose much fund by transaction fee. so if we do arbitrage try to find the difference in price and high trading volume to avoid the falling price very far.
Well, of course that is the basics, but it is very infrequent to find such differences, except in coins with very low volume or in EDS (EtherDelta Sucks), or probably in some other decentralised exchanges.