There are different ways to make simple loops. The way I like to make loops is to bend the wire 90 degrees, then grasp the very end of the wire in the round nose pliers and roll the wire around into a loop. At this point small adjustments need to be made to make the end fit well to the shank. Sometimes you need to round the loop more, sometimes you need to re-establish the angle of the original 90 degree bend, sometimes you need to do both.
This method requires that you know about how much wire you need to make the size loop you want. The outer diameter of the loop x 3 is a good starting point for this measurement. After you have made lots of loops this becomes more instinctive.