Have you ever given a performance where you have tried really hard to make those quiet dynamics only to find that the notes don’t come out? You then try to creep back in only for another note not to sound! Oh dear, this is the practice method for you.
For this practice method you need to make the whole of your piece sound more confident. To do this you need to go through your piece and mark all the dynamics up one notch. So each time you see an mf you need to mark this up to f. Each time you have a p you need to mark this up to mp and so on. You will need to do this in any case to allow for being accompanied.
Now for the playing, pay careful attention to your new dynamics and make sure that you play with a good full sound all the time.
When you come to perform you will find that these bolder dynamics will give you more confidence. Also as dynamics are relative the audience will be none the wiser!