If you are nervous about hitting the curb with your front wheel you can practice this at first by going over a parking stall line but be careful to keep your front wheel straight when you lift it up.
A more advanced technique for getting up the curb is to pedal your way up. To Practice this, approach the curb at a much slower speed while standing with your pedals in the 2 and 8 O’clock positions and lift your front wheel up to the top of the curb as described above. Just as your rear wheel contacts the curb crank your pedals to the 12 and 6 O’clock position bringing the rear wheel to the upper level.
These are very effective techniques for clearing obstacles on the trail at slow speeds.