I think we all need practice which is created for personal needs. The challenge of learning an instrument is getting through the obstacles we face in our daily practice.
When most students start out, a minimum of 15 minutes and a maximum of 45 minutes at any given practice session should be enough to get going. Decide how much time you have and how tired you are on the day and divide up your time into four sections, scales, sight reading, technical exercises and finally pieces. Keep the ratios similar whether you are practicing for 15, 30 or 45 minutes.
A suggestion for students is to practice every day and have one day off or two potentially, if they don't practice on the day of their lesson.
Start with scales. Why? Scales will warm your fingers up..
Remember, practicing is not playing! You can make mistakes, in fact this is the ideal opportunity to do so. We are NOT playing or performing when we practice.
NOW SIGHT READING!
Then, follow with a new sight reading piece. Here you can work on rhythm and incorporate some technique. Playing some separate finger technique exercises like Czerny, will also transform your playing quite quickly giving you greater accuracy and speed.
FINALLY YOUR PIECE :)
Finally, when you come to practise your pieces. Take weak sections and make the mistakes until you get things right!
Remember that consistency is the key!