Using Google Analytics to Monitor Checkout Abandon Rates at Each Stage
Here's a simple way of spotting problems with each stage of your checkout in one glance. The key is to make a series of micro-funnels in Google Analytics, one for each step in the checkout journey.
Then you put the abandon rates for each of those funnels on a GA Custom Dashboard. Result: you can see any odd spikes in the abandon rate with just one glance.
That description may be enough to get you going. But if you'd like more detail, I've written a full explanation with a how-to video here: