How to Determine Total Ink Coverage in Photoshop

Click on the Info Palette (F8), then click the upper right arrow to change Palette Options:

Change Second Color Readout Mode to Total Ink and click OK:

Now when you move the cursor over your image, the value will change, which corresponds to total ink. You do not want total ink to ever be more than 300%. Note than in the example below, the Magenta and Yellow values are too high, therefore the total ink value exceeds the 300% limit: