Go slower
Often it may be better to slow down, and spend more time doing things like naked cuddling. These build sexual energy and also increase levels of Oxytocin, the “love hormone” inside the male body. Oxytocin has been shown to increase erection duration, and shorten the time needed between sexual acts.
Source: http://humupd.oxfordjournals.org/content/12/4/437.long