For me, what helped was practicing each hand separately, then slowly putting them together. Start with a slower speed, then speed up as your accuracy increases.
Plus check your technique. Bad technique kept me from getting songs up to tempo no matter how much I practiced. Make sure that you are not playing by moving your fingers up and down. Use arm weight and gravity. Check out some of Sam Tolbert's Youtube videos. Also watch ddw4e play "I Know The Bible Is Right" on Youtube. Notice the fingers do not go up and down. I am working with a piano teacher concentrating on technique and the difference in my playing is night and day.
Break up your song into very small parts making sure you focus on the parts that are slowing you down.
I start off slow to make sure I have the right notes. But after I know I have the right notes, I jump to a fast tempo because you use a different technique at a fast tempo than a slow tempo. If you miss notes, then work on that section until you can play it fast. Do not try to play the whole song until you can accurately play the sections that are a problem to you.
