If you have trouble with hitting the correct notes, try using some different rhythms, such as dotted eighth-sixteenth notes rather than straight eighth notes for example. Or you can try taking the notes out of rhythm until you can play the interval easily. For rhythmic accuracy, slow down. A lot. Once you are comfortable with it, gradually increase the speed. For trouble with playing with both hands at once, first play the bottom line, then play the top line, and then put them together. Don't try to play both right away. I HIGHLY recommend playing scales. Just DO NOT play the same ones every time, and change how you play them each time. Use different rhythms and tempos. My last bit of advice is to always use a metronome. This will help you play at a constant tempo and when performance time comes, you should have a developed inner pulse. Also check out this blog [url=http://www.bulletproofmusician.com]here[/url]. I have found several bits of advice from it.