THis is my advice from another thread!
Think of it this way. Your front foot is the accelerator, more weight on the 'planing' part of the board will make you go faster. You've probably seen the pros bouncing the board, they are basically increasing pressure on the front of the board to get it to go faster.
The back foot is the brake. And this is the key to the bottom turn. If you can bear to wipe out once more, try this: Catch a wave, get up, then put all your weight on the back foot (whilst keeping your balance and not falling off) you will notice that the wave overtakes you. If you feel the 'tail' of a board, you will feel that the edges tend to be quite sharp/ hard. As you move down the rails towards the nose, the edges become more rounded.
The key to the bottom turn is to get the balance between tail and nose right. You will notice that the opening bottom turn of most pros tends to be a sweeping arc rather than a quick turn.
If you put too much weight on the tail in the bottom turn, you are basically driving the hard edge of the rails into the water and slowing the board right down, by the time the wave reaches you, you have no forward momentum and the wave will overtake you.
Hope this helps