It used to be a lot easier a few years back. Now there's lots of bots out there trying to arbitrage.

Nevertheless, try to search for arbitrage during large market movements. I find that when prices fly either up or down, not all exchanges manage to move in tandem, hence you get an arbitrage opportunity.

One other thing to consider though is that you have to have your funds allocated correctly in order to actually capitalize on the opportunities. You might want to split your funds/coins between a few exchanges that you think you might be using.